How to Build a PC: Components, Assembly and First Boot

Building a PC is easier than it looks: the connectors only go in one way and the actual assembly takes a couple of hours. The real work happens beforehand, when choosing components that are compatible with each other. During assembly, there are two delicate steps: installing the processor and applying thermal paste.

Today, there are two desktop platforms: AM5 for AMD, featuring Ryzen 7000 and 9000 series processors, and LGA1851 for Intel, with Core Ultra Series 200. Both use only DDR5 memory: the DDR4 from an old computer won’t fit, which is the first mistake to avoid when repurposing parts.

There is a difference in platform longevity that you should know about. AMD has promised to support AM5 for several more years, so in a while, you will be able to upgrade just the processor. Intel, on the other hand, will move to a new socket, LGA1954, with Core Ultra Series 400 expected between late 2026 and early 2027: an LGA1851 board bought today won’t accept processors from that generation.

Components and how to choose them #

Component	Purpose	What to check
Processor	Performs all system calculations	Socket compatible with the motherboard
Motherboard	Connects all the parts	Socket, form factor (ATX, microATX, mini-ITX), ports, and slots
RAM	Holds the data the PC is working on	DDR5, speed supported by the motherboard
Graphics card	Graphics and gaming	Length compatible with the case, power consumption
Storage	OS and data	NVMe SSD for the operating system
Power supply	Provides power to everything	Adequate wattage, certification, reliable brand
Case	Holds everything	Motherboard form factor, space for cooler and graphics card
CPU Cooler	Cools the processor	Socket compatibility, maximum case height

To make a mistake-free list, you can use PCPartPicker: it automatically flags incompatibilities between sockets, form factors, and dimensions, and compares prices from Italian retailers.

Three checks will save you from almost all problems:

Socket and chipset. The processor must have the same socket as the motherboard. For AMD, the most common chipsets are B650, B850, X870, and X870E; for Intel, H810, B860, and Z890.
Dimensions. Compare the graphics card length and the cooler height with the case limits. This is the most frequent reason for returns.
Power supply. Give yourself a bit of breathing room regarding estimated power consumption and don’t skimp on this part: if a low-quality power supply fails, it can take other components down with it.

ATX motherboard viewed from above with the processor socket, RAM slots, and edge connectors — You can identify the socket, RAM slots, and form factor on the motherboard: these are the three pieces of information to check before buying

Check the BIOS before buying. On the motherboard manufacturer’s website, you’ll find a list of processors supported with the required firmware version: sometimes a board sold today needs an update to recognize a processor released later. Many recent boards can also be updated without a processor via a dedicated USB port (called BIOS Flashback or similar). If your processor is very new, look for this feature.

Getting ready #

You will need a Phillips head screwdriver with a magnetic tip, a large and well-lit table, and the component boxes within reach: they contain screws, adapters, and manuals that you will use.

Computer hardware components laid out in order on a table before assembly — Laying everything out in order before starting prevents you from searching for a screw halfway through assembly

You only need a few precautions to handle static electricity: touch a metal object before handling parts, don’t work on carpets or blankets, and hold the boards by the edges. An anti-static wrist strap helps, but it isn’t essential under normal conditions.

Assembly order #

The processor, memory, and cooler should be installed with the motherboard outside the case, resting on its box: it is much more comfortable this way.

RAM modules inserted into the motherboard slots with the clips engaged — The modules are properly seated when the side clips snap into place by themselves

Processor. Lift the socket lever, align the small triangle etched on a corner of the processor with the one on the socket, and set it down without pressing: it should drop in on its own. Lower the lever; some resistance is normal. If the processor isn’t sitting flat, do not force it, as it is misaligned.
Memory. Open the slot clips, align the notch on the module with the one in the slot, and press down on both ends until the clips snap shut. With two modules, your manual will tell you which slots to use: usually the second and fourth from the processor. Using the wrong slots can lead to poor RAM performance.
NVMe SSD. Slide it at an angle into the M.2 slot and secure it with the tiny screw or the quick-release latch. If there is a heatsink over the slot, remove the protective film from the thermal pad.
Thermal paste and cooler. You’ll find everything in the section below. Remember to connect the fan cable to the CPU_FANheader.
Motherboard in the case. Check that the standoffs at the bottom of the case match the holes on the board: one extra standoff in the wrong place can cause a short circuit. Also, check the rear I/O panel: on modern boards it’s already attached, but on budget ones, you must install the metal I/O shield into the case first from the inside.
Power supply. It goes at the bottom of the case, usually with the fan facing down if there is a vent underneath.
Power cables. The 24-pin for the motherboard, the 8-pin at the top for the processor (this is often forgotten, and without it, the PC won’t turn on), and the ones for the graphics card.
Graphics card. Save this for last because it’s bulky and will get in your way. Remove the expansion slot covers from the back of the case, slide it into the main PCIe slot until the latch clicks, and screw it in. High-end cards use the 12V-2x6 connector (the 16-pin one): push it all the way in, and don’t bend the cable immediately after plugging it in.
Case cables. Power button, LEDs, front USB, and audio ports. The motherboard manual tells you where they go: this is the most tedious part, and the only one where you absolutely need the manual.

Applying thermal paste correctly #

This is where mistakes happen more than anywhere else, and an error here can haunt your PC for its entire lifespan with high temperatures and noisy fans.

If the cooler is new, it usually comes with pre-applied paste on the base—a gray rectangle. In that case, do not add any and do not remove what’s there.

If you are applying it yourself, all you need is a drop in the center of the processor, about the size of a grain of rice or slightly larger. Don’t spread it: the pressure from the cooler will distribute it for you. If you use too much, it acts as an insulator instead of a conductor and risks leaking onto the contacts.

A pea-sized drop of thermal paste in the center of the installed processor — The correct amount: just one drop in the center, without spreading it

Tighten in a cross pattern. Tighten the four screws slightly at a time, alternating between opposite corners so that pressure remains even. If you fully tighten one screw at a time, the heatsink will tilt and leave an uncovered area.

If you remove the heatsink, wipe off the paste and reapply it from scratch: once detached, the layer won’t be uniform again. Clean with isopropyl alcohol and a lint-free cloth.

Never turn on the PC without a heatsink, even “just to see if it boots.” Modern processors have thermal protections, but temperatures can spike in just a few seconds.

The first boot #

Before closing the case, connect your monitor, keyboard, and power supply, then turn it on. If the BIOS screen appears, the assembly was successful. The first boot with DDR5 can take one or two minutes of black screen while the motherboard “trains” the memory: wait a bit before assuming there is a fault.

Then, three things:

Enable the memory profile. By default, RAM runs slower than its rated speed: in the BIOS, the EXPO (AMD) or XMP (Intel) setting sets the correct speed with one click.
Check that everything is recognized: memory capacity, drives, and CPU idle temperature.
Set the boot priority to your USB drive containing the operating system.

For Windows 11, prepare the USB drive on another computer using the Microsoft Media Creation Tool. You will need a license, which must be purchased separately if the PC is new; if you are using Linux, you don’t need to buy anything.

If it doesn’t turn on #

Symptom	Most likely cause
No signs of life	8-pin CPU cable not connected, or the power supply switch is off
Fans spinning but no image	RAM not properly seated: remove and reinsert it, pressing until it clicks
No image with the graphics card installed	Monitor plugged into the motherboard instead of the graphics card
Turns on and immediately shuts off	Short circuit: check the standoffs under the motherboard
Beep codes or diagnostic LEDs lit up	The motherboard manual explains what they mean: this is the fastest way to identify the problem

FAQ #

Is it still worth building a PC instead of buying a pre-built one? #

The price advantage has shrunk because pre-built manufacturers buy components in bulk, and since late 2025, RAM and SSD prices have increased significantly for everyone. Two solid advantages remain: you choose every single part, avoiding the hidden savings on power supplies and motherboards typical of pre-built PCs, and you know exactly what’s inside, making it much easier to upgrade or repair.

What tools do I need? #

A medium-sized Phillips screwdriver with a magnetic tip is enough for almost everything. It’s also useful to have some cable ties to organize your wires, a flashlight, and—if you need to reapply thermal paste—isopropyl alcohol and a cloth.

How long does it take the first time? #

Between two and four hours if you take your time and read the manual. Someone who has done it before can do it in an hour. Avoid doing it late at night: most mistakes happen in the last half-hour when you are tired.

Can static electricity break a component? #

It can, but the risk is often exaggerated. Touching metal before you start, avoiding carpets and rugs, and holding the boards by the edges is enough in most cases. The risk increases in very dry environments, such as in winter with the heating on.

How much power should the power supply have? #

Add up the power consumption of your CPU and graphics card, add about a hundred watts, and round up. For most gaming PCs, it’s between 650 and 850 watts; more for ultra-high-end graphics cards. Focus on quality over wattage: a certified power supply from a reliable brand is better than a higher-wattage one from an unknown brand.

Do I still need the I/O shield? #

On mid-range and high-end motherboards, no—it’s already integrated. On budget boards, it comes separately and must be installed in the case before the motherboard: if you realize you forgot it later, you’ll have to disassemble everything.