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Ten common mistakes made when building a PC , even by experienced users, due to lack of knowledge or carelessness . The aim is to help avoid problems during assembly and ensure optimal performance of the computer .

Building a PC today is much easier than it was several decades ago, but even so, it’s not uncommon to encounter mistakes , even among the most experienced users. Often, these errors stem from a lack of knowledge, but they can also be caused by simple oversights.

Over the past fifteen years I have encountered some very curious cases, even among professionals in the sector, and that is why I have decided to write this article, where I will share with you the ten most common mistakes made when building a PC .

In this list of ten mistakes, I’ll explain why they occur, how they can affect your team, and what you can do to avoid them . Ready? Then get comfortable, because we’re about to begin.

1.- Hardware incompatible

This is one of the worst mistakes we can make, because we won’t be able to finish assembling the PC and it won’t work.  We’ll have to return the incompatible components, if possible, and buy new ones that are compatible.

Hardware incompatibility in PCs occurs when we try to assemble components that are not compatible , and it can happen in four different ways :

• Electrical incompatibility: This is one of the most common issues, and it occurs when components that, although physically compatible, have different power requirements are used. For example, Intel Coffee Lake-S processors use the LGA1151 socket, the same as Intel Kaby Lake, but they are electrically incompatible and only worked with LGA1151 motherboards with a 300 series chipset.
• Form factor incompatibility:  This is also very common and occurs when components, although they have the same power requirements, have dimensions that make them incompatible. For example, a large graphics card will be electrically compatible with any motherboard, but may be incompatible with many small form factor cases.
• Absolute incompatibility: This occurs when both of the previous incompatibilities are present, meaning that two or more components are incompatible at both the electrical and form factors levels. For example, a Threadripper processor and an AM4 motherboard would have this level of incompatibility, as would a motherboard with DDR4 memory slots and a DDR5 memory kit.
• Minor incompatibility occurs when we use components that work together seamlessly, but with limitations that prevent us from achieving their maximum performance. This would happen, for example, if we install DDR5 RAM with an overclocked profile of 9,000 MT/s on a motherboard that doesn’t support it; it would work, but at a lower speed. Similarly, if we install a PCIe Gen5 SSD in a slot limited to PCIe Gen4, it would also work, but at a reduced speed.

How to avoid this mistake

1. Take into account the dimensions of the chassis where you are going to assemble the PC, and check that all components are compatible in terms of format (measurements and size).
2. Make sure all components are compatible before you buy them. It’s easy, because manufacturers provide compatibility lists in their product specifications.

2. Installing the fans incorrectly

It’s not a serious mistake, but it can be very annoying , and we might not even realize it until some time has passed.

The fans are designed to clearly indicate their orientation for whether they should be drawing air into or exhausting the chassis . If the fans are installed incorrectly, they will operate in the opposite way to intended.

For example, imagine you want to install three fans at the front of the case drawing air in and one at the back exhausting air. If you make the mistake of installing them incorrectly, they will do the exact opposite: you’ll have three fans at the front exhausting air and one at the back drawing air in.

This can affect the airflow inside the chassis, and have a negative impact on component temperatures .

How to avoid this mistake

1. Check the fans carefully before mounting them and remember the correct orientation.
2. If you have any doubts, follow this simple rule: if the “pretty” side of the fan faces outwards from the chassis, it will be bringing air in, and if it faces inwards from the chassis, it will be pushing air out.

3. Using an insufficient cooling system

It’s a problem I experienced firsthand not long ago. A friend asked me to build him a PC, but to save money he insisted on using the stock cooling system that came with the Intel Core i5-12400F, something I told him wasn’t a good idea because:

• In his village, the summer heat is so high that it is normal to exceed 40 degrees C.
• The internal airflow of the equipment was very weak, because it only had two fans, one in the front bringing in air and one in the back expelling air.

The fan that comes with the Intel Core i5-12400F is very basic, and as soon as the processor reaches 50% or more load, its power consumption increases, the temperature rises , and unless we are in a very cold space, we will find temperature values ​​that can exceed 80 degrees C.

In his case, while playing Counter-Strike 2, he experienced temperatures exceeding 90 degrees Celsius and even suffered some restarts. Replacing the original fan with a €14 one solved the problem.  It’s not worth taking these risks to save a few euros.

The cooling systems that come with modern processors are often insufficient . Even when they are adequate, it’s better to invest a little more in a higher-quality cooler for better temperatures and less noise.

How to avoid this mistake

1. Keep in mind that most processors have a turbo mode, and that their actual TDP is higher than the base TDP indicated by the manufacturer.
2. Check the processor’s maximum TDP, which refers to the turbo mode value. For example, a Core i9-14900K has a base TDP of 125 watts and a turbo mode TDP of 253 watts. That’s more than double the difference.
3. Purchase a cooling solution that is capable of dissipating the heat generated by a value higher than the maximum TDP of your processor.

4. Incorrectly installing the RAM modules

Installing the RAM modules is not complicated; we just need to orient them correctly, align them, and push firmly until we hear the click of the retention system.

However, if we want to ensure maximum stability, achieve an optimal configuration, and take advantage of the dual channel, we must install it in a specific way .

To activate dual-channel RAM, you must install the RAM modules in alternate slots, or alternatively, fill all the slots on the motherboard. If you have a motherboard with four slots and install two RAM modules in slots 1 and 2, or in slots 3 and 4, you will not have activated dual-channel RAM.

When we activate dual channel, the RAM communicates with the CPU through a 128-bit bus, while in single channel it works with a 64-bit bus, which negatively affects performance and can make a considerable difference, especially if we use an integrated graphics card, which will use the RAM as VRAM and depend on its bandwidth to develop its maximum performance.

How to avoid this mistake

1. If your motherboard has four RAM slots, prioritize using slots 2 and 4.
2. Always install RAM in alternate slots. To enable dual channel, you must install two modules in slots 1 and 3 or in slots 2 and 4.

5. Installing an unsuitable power supply

The power supply, along with the motherboard, is the cornerstone of any PC. Many people still don’t fully grasp this, but we need to be aware of it and give it the importance it deserves.

Installing an unsuitable power supply is one of the most serious mistakes we can make when building a PC, because:

• It can compromise PC performance and stability.
• In extreme cases it can “die” and take other components with it.
• It can cause incompatibilities with other components, both due to lack of power and because it does not have the cables and connectors we need.

If your power supply doesn’t provide the actual power your PC components need, it might work for a while, but it will eventually cause problems, and the power supply will eventually suffer irreversible damage. This type of electrical failure can cause electrical damage to other components.

How to avoid this mistake

• Be clear about the power connectors and cables you will need.
• Assess the overall power consumption of your PC components and choose a power supply that exceeds that value by at least 25%. For example, if your PC will consume an average of 600 watts, ideally you would install a 750-watt power supply.
• Only buy power supplies from reliable brands and with a minimum quality standard.

6. Incorrectly connecting the wiring

Of all the mistakes we can make when building a PC, this is probably the most frequent ; in fact, it is common even among experienced users.

The complexity of building a PC will largely depend on the components you use . Building a PC with 12 fans, RGB LED lighting, and liquid cooling is not the same as building one with three fans and an air CPU cooler.

A more complex setup carries a greater risk of making mistakes when connecting the wiring. The most common cases are:

• Forgetting to connect the CPU power cables to the motherboard.
• Do not connect the fan power cables.
• Incorrectly connecting the cables on the front of the chassis.
• Forgetting to connect a specific cable, especially in components that use multiple cables.

Depending on which cable we forget to connect, the consequences can be more or less serious . For example, if we connect the chassis wiring incorrectly, the power button might not work, and neither might the front USB connectors.

If we don’t connect the CPU power cables, we could have performance and stability problems , and if we don’t connect fan or cooling system cables, we run the risk of encountering abnormal temperatures, which could lead to stability problems.

How to avoid this mistake

1. Identify, component by component, the cables you need to connect.
2. Find where each of those cables should be connected, and memorize it or write it down.
3. Connect each cable in an orderly fashion, and check that you have used the correct connector before moving on to the next component or cable.
4. Before closing up and turning on your PC, do one last check of the cabling.

7. Do not use a support base for the graphics card

Most modern graphics cards are quite large and heavy . Motherboard manufacturers have responded by reinforcing PCIe slots with metal, but even so, using a support pad is highly recommended, even with mid-range graphics cards.

If we are going to use high-end graphics cards, such as the GeForce RTX 5070 Ti and above, and the Radeon RX 7900 XT and above, a support base is essential, because these graphics cards are very large and heavy, and over time they can not only deform the PCIe slot, but also suffer deformations in their own PCB.

These deformations occur over time due to the weight and length of the graphics card, and can damage the motherboard and the card itself , eventually leading to a point where they may stop working properly.

For example, a graphics card like the AORUS GeForce RTX 5090 Master ICE, which is enormous and very heavy, must be accompanied by a support stand . In the case of a dual-fan GeForce RTX 5060, such a stand wouldn’t be necessary, but if we’re going to install a larger and heavier triple-fan model, it would be advisable.

How to avoid this mistake

1. Use the graphics card in a vertical position.
2. Always mount a support base when using a graphics card longer than 24 cm that occupies two or more slots.

8. Applying the thermal paste incorrectly

This mistake is still very common because there are still some myths about thermal paste , and because many people do not understand that the processor format determines the optimal application method.

If the thermal paste is applied incorrectly, it may not completely cover the processor’s IHS. We might also apply too little, or conversely, apply too much.

If we do not apply enough thermal paste, or if the amount is insufficient, we will most likely encounter abnormally high temperatures due to poor heat transfer between the processor and the contact base of the cooling system.

It’s always better to apply more thermal paste than necessary than too little, but if you use too much, it could spill onto the socket and reach the motherboard . If this happens and the paste isn’t conductive, you won’t have to worry about serious damage, but if it gets onto the socket pins, it can affect their contact with the CPU and cause serious problems until you clean it up.

How to avoid this mistake

1. Apply the thermal paste correctly according to the shape of the processor’s IHS:

• If it’s square, like the Intel Core Gen11 and earlier and the Ryzen 9000 and earlier, simply apply a small ball of thermal paste to the center.
• If it’s rectangular, like the Core Gen12 and above, the ideal thing to do is to make an “X” with the thermal paste from the corners of the IHS.
• In the case of very large processors, such as AMD’s Threadripper, we will need to make an “X” from the corners and reinforce the four gaps of that “X” with a small ball of thermal paste in each one.

2. Use the correct amount of thermal paste, keeping in mind that it is always better to use a little too much than too little.

9. Do not remove the sticker from the base of the cooling system

Undoubtedly one of the simplest and most frequent mistakes we make when building a PC. Many cooling systems, especially AIO liquid cooling kits, come with plastic stickers that protect the copper contact base, and they clearly indicate that we should remove them.

The problem is that in many cases, due to haste, nerves, carelessness, or a bit of all three, we may forget to remove that sticker, and if this happens, we will end up turning on the equipment with it still on.

At first, you won’t notice anything unusual, but as soon as you start using demanding applications or games, you’ll realize that performance is far below expectations and the CPU temperature is too high . This is because the sticker is preventing proper heat transfer between the processor’s IHS and the contact base.

We will have no choice but to turn off the equipment, remove the contact base of the cooling system, remove the sticker, reapply thermal paste and reassemble the cooling system.

How to avoid this mistake

1. Position the cooling system so that you can see the sticker directly.
2. Before applying the thermal paste, get into the habit of reinforcing the contact base so you don’t forget to remove the sticker.

10. Unbalanced components

Unbalanced components and incompatible components are two different things. The former are those that work fine in a specific PC build, but whose power and performance don’t match the rest of the components , and which can therefore cause significant imbalances and stability or performance problems.

For example, pairing an Intel Core i3-12100F with a GeForce RTX 5090 graphics card would be a serious imbalance , because the former will create a tremendous bottleneck and prevent the latter from reaching its full potential, thus reducing the graphics card’s performance.

Another example, but the reverse, would be pairing a Ryzen 9 9950X3D with a GeForce RTX 5060. In this case, we would have an outstanding processor with a graphics card that wouldn’t be up to par.

We can also find other significant imbalances in different components . Here are some more examples:

• Installing a motherboard with an insufficient VRM will reduce processor performance.
• Installing too little RAM will affect the overall performance of the computer and prevent us from running certain applications and games.
• Installing slow RAM will affect processor performance and integrated GPU performance.
• Installing a slow storage drive: can affect overall system performance.

How to avoid this mistake

1. Be clear about your budget and the use you want to give to the equipment.
2. Building on the previous point, distribute your budget evenly. For example, if you’re going to use it for gaming, you should invest at least a third of your budget in the graphics card, and the processor should cost you approximately half of what you pay for your graphics card.
3. Slightly favoring one component can be a good idea, as long as you don’t fall below a minimum threshold. In this regard, if you’re building a gaming PC, it can be helpful to use the recommended requirements of most current games as a reference to ensure you don’t go below them: a 6-core, 12-thread CPU, 16 GB of RAM, a GeForce RTX 4060 or Radeon RX 7600 graphics card, and an NVMe SSD.

Sources: https://blog.elhacker.net/2025/12/diez-errores-frecuentes-al-montar-un-pc.html