My PC is slow: the real causes and fixes (laptop or desktop)

"My PC is slow" is probably the sentence I hear most often at the workshop. And yet that simple complaint hides very different causes: a worn-out hard drive, an overheating processor, too little memory, software running in the background. Cleaning up temporary files is often just a surface fix.

This guide applies to laptops and desktops alike. It starts with the checks you can run yourself, for free, in half an hour. They are often enough to find the real cause, and therefore the right fix.

Free checks you can run yourself#

The paths below are those of Windows 11. Do them in order and write down what you see: the table in the next section tells you what it means.

1. 1
   See what is working. Open Task Manager (Ctrl + Shift + Esc), Processes tab, and sort by CPU, then Memory, then Disk. An unknown program using the processor while you are doing nothing is suspicious. If the disk stays at 100%, the Disk column shows which process is using it: Windows Update, the antivirus or an app can keep it busy for a while after startup. If nothing explains it and it lasts, the drive itself becomes the suspect, especially a mechanical one (next check).
2. 2
   Check the drive type. In Task Manager, Performance tab, click Disk 0: Windows shows SSD or HDD. An HDD (mechanical hard drive) is the most common cause of slowness I come across.
3. 3
   Turn off unnecessary startup apps. Task Manager, Startup apps tab (or Settings, Apps, Startup). Disable what you don't use every day: messaging, music, manufacturer utilities. Keep your antivirus enabled. A name you don't recognise should be neither kept nor disabled blindly: check its publisher (Publisher column), search for its name online, then run the antivirus scan from check 6. Anything that serves your hardware (audio driver, touchpad, graphics card) can stay enabled once identified.
4. 4
   Free up space. Settings, System, Storage, then Cleanup recommendations. A nearly full C: drive slows Windows down and blocks its updates: keep some headroom, ideally at least 10 to 15% free space.
5. 5
   Install updates. Settings, Windows Update, Check for updates, then restart. Drivers offered by the manufacturer are in Windows Update, Advanced options, Optional updates: they are not installed automatically.
6. 6
   Run a full antivirus scan. Windows Security, Virus & threat protection, Scan options, Full scan. If doubt remains, then choose Microsoft Defender Antivirus (offline scan): the PC restarts, scans itself without loading Windows, then restarts on its own.
7. 7
   On a laptop, check the power mode. Settings, System, Power & battery, Power mode. In a power-saving mode the processor is deliberately held back: compare on mains power in Balanced mode.
8. 8
   Measure the temperature. Install HWMonitor (free, published by CPUID, at cpuid.com), use the PC normally for 15 minutes and check the processor temperature. Compare it with the maximum temperature for your processor model, shown on its spec sheet at Intel (TJUNCTION) or AMD (Tjmax): it varies from one model to another. A processor that gets close to it during simple office work or browsing can point to clogged cooling, or to a program running in the background: check Task Manager too.

What your findings mean#

If several rows apply to you, start with the drive: it is the most common cause and the most dramatic one to fix.

The most common culprits#

1. A mechanical hard drive (HDD)#

This is by far the number one cause. If your PC is more than five or six years old and has never been upgraded, it very likely has a mechanical hard drive: the little clicks you sometimes hear at startup, that's it.

These drives use platters spinning at 5,400 or 7,200 rpm and a mechanical read head. Slow by nature, they get even slower with age, and Windows 11 isn't designed for them.

Fix: replace it with an SSD. It's the upgrade that changes performance most radically: a PC that took several minutes to boot starts in a few dozen seconds. Fitting starts at €30 in labour at the workshop, depending on the device, plus the price of the SSD (see the budget below).

2. Not enough RAM#

RAM is your PC's working memory, the one that holds open programs. Windows 11 alone uses 2 to 3 GB at idle. With 4 GB in total, a browser, a few tabs and a video call are enough to fill it: Windows then starts using the drive as backup memory, which is much slower.

Practical thresholds:

• 4 GB: not enough today for everyday use
• 8 GB: comfortable minimum for office work and browsing
• 16 GB: recommended if you keep several applications open
• 32 GB and more: video editing, gaming, virtualisation

Fix: add RAM. Fitting starts at €30 in labour, depending on the device, plus the memory modules. Watch out: many recent laptops have RAM soldered to the motherboard, with no way to add more. A desktop, on the other hand, almost always has free or replaceable slots.

3. Overheating and thermal throttling#

A PC that runs too hot automatically slows its processor down to avoid damage. This mechanism is called thermal throttling.

Typical symptoms:

• The PC is fine at startup, then slows down after 15 to 20 minutes of use
• The fan runs flat out all the time
• The keyboard area (or the back grille of a tower) is very hot

Two causes, often together: the thermal paste between the processor and its heatsink has dried out over the years, and the fan or heatsink is clogged with dust.

Fix: a full clean and a thermal paste replacement, €65 at the workshop for a laptop as well as a desktop (€45 for a clean without new paste).

4. Malware or bloatware#

A virus, spyware or a cryptocurrency miner can take a large share of the processor in the background. Your PC then crawls even when you're doing nothing.

Bloatware (useless preinstalled software that launches at startup) has a similar effect, without being malicious.

Fix: checks 3 and 6 above. If pop-ups or an unknown program keep coming back, virus analysis and removal costs €35 at the workshop. In severe cases, a clean reinstall of Windows is safer than any clean-up.

5. An ageing Windows#

Over time Windows piles up half-uninstalled software, drivers replaced several times, forgotten background tasks. It's rarely the main cause, but it adds up.

A clean reinstall of Windows fixes this, as long as the hardware problems are fixed first: reinstalling Windows on a tired hard drive or on an overheating PC changes nothing in the long run.

6. A worn battery (laptops)#

On some models, a badly worn battery leads the manufacturer to throttle the processor, sometimes even on mains power. To check yours, type powercfg /batteryreport in Terminal: Windows generates a report comparing the current capacity to the original one.

Budget to get a PC back in shape#

Workshop rates (labour, parts extra), the same as on the pricing page:

Parts are paid separately, and their price has risen sharply since late 2025 because of a global memory shortage affecting RAM and SSDs alike. So I price memory modules and SSDs case by case, for your PC's exact model.

The quick quote, without disassembly, is free. A detailed assessment with disassembly costs €25, deducted from the final price if you go ahead with the repair.

What not to do#

• Disable your antivirus to "gain speed": a very bad idea, for an unnoticeable gain
• Install "optimisers" or registry cleaners: useless at best, harmful at worst (ads, fake problems detected to sell you a licence). The tools built into Windows are enough
• Defragment an SSD: pointless, Windows optimises SSDs by itself
• Format without diagnosing: if the problem is hardware (drive, RAM, overheating), reformatting won't change anything

When to consider a new PC#

Repair or an upgrade is generally worth it if:

• the PC can move to Windows 11. Microsoft requires, among other things, a processor on its list of compatible models, a TPM 2.0 security chip, UEFI Secure Boot, 4 GB of RAM and 64 GB of storage (full requirements). The easiest way to find out: Microsoft's free PC Health Check app and its Check now button, which also tells you what is blocking;
• your use is everyday: office work, browsing, video, video calls;
• the motherboard and screen are healthy.

The Windows 10 case. Its support ended on 14 October 2025. Home users enrolled in the Extended Security Updates (ESU) programme still receive security updates until 13 October 2026, and nothing after that. A PC that can't move to Windows 11 can feel pleasant again with an SSD, but it will stay on a system with no security fixes. There is an alternative: installing Linux (Ubuntu, Linux Mint…), lightweight and up to date, which I install and set up at the workshop.

Beyond that, if the processor is really outdated or the motherboard is failing, a new PC is often the more sensible choice. I always run this calculation with the customer before any work: there's no way I'm letting you spend €150 on repairs for a PC worth €80.

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