How to Check a Second-Hand Desktop PC Before Buying
A desktop hides its faults better than a laptop, because the parts you can see are rarely the parts that fail. A clean case tells you nothing. What matters is the monitor, the peripherals, and whether the machine stays stable once it is warm.
Test the monitor as a separate purchase
If the deal includes a monitor, treat it as its own transaction. A dead panel is the single most expensive thing in a desktop bundle and the easiest to check.
Open the dead pixel test and run through the solid colours full-screen. White finds dark dead pixels and dust. Black finds bright stuck pixels, backlight bleed and, on an OLED, uneven ageing. Red, green and blue isolate individual subpixels — a dot that vanishes on one colour but not the others is a failed subpixel rather than a fully dead one.
Then check the refresh rate actually matches what the seller claims. A monitor advertised as 144Hz that Windows is driving at 60Hz might be a cable problem or might be a panel that was never 144Hz. The refresh rate test measures what the display is really doing, not what the box said.
Peripherals are where sellers quietly round up
"Comes with keyboard and mouse" covers a wide range of conditions. Both are cheap to replace, but you should know before you pay rather than after.
- Keyboard: the keyboard test catches dead keys immediately. Press every one, including the function row and the numpad. Watch for keys that fire twice from one press — switch chatter gets worse over time.
- Mouse: run the double-click test. A mouse switch that registers one click as two is the most common peripheral failure and the most annoying to live with.
- Audio: plug headphones into the front and rear jacks and run the speaker test. Front-panel audio is wired through a separate header and frequently is not connected at all.
The checks that need the machine running
Ask to see the machine boot from cold, not already switched on. A desktop that has been warming up for an hour before you arrive is hiding something, and the most common something is a boot problem.
Once it is up, open Task Manager on Windows and look at the Performance tab. Confirm the CPU, RAM and GPU match what was advertised — not the sticker on the case, which is often from the original build and not the current parts.
Then leave it under load. Play a video at full screen, open a dozen browser tabs, and listen. Fan noise that rises and stays high at idle usually means dust or a failing fan. A machine that reboots under load has a power supply or thermal problem, and both are real money.
What to look at inside the case
Ask to open the side panel. You are not diagnosing components, you are looking for three things:
- Dust. A heavy dust blanket on the heatsink and fans means years of running hot. It is cleanable, but it tells you how the machine was treated.
- Bulging or leaking capacitors on the motherboard — small cylinders with domed or crusty tops. That is a motherboard at end of life.
- Mismatched or missing screws, cut cable ties, thermal paste smeared outside the CPU block. None of these are faults on their own; together they say the machine has been worked on by someone in a hurry.
A seller who refuses to open the case is telling you something.
Storage is the quiet failure
A failing drive gives almost no warning in a short demonstration. Ask how old the drive is and whether it is the original. If the machine is more than four or five years old and still on its first mechanical hard drive, assume you will replace it — budget for it rather than being surprised.
An SSD that has been used heavily for years has finite write endurance. Neither of these is a reason to walk away from an otherwise good machine, but both belong in the price.
What is worth fixing
Dust, a failing case fan, a worn mouse and a tired hard drive are all cheap and expected on a used desktop. A dead monitor panel, a failing power supply, or a motherboard with swollen capacitors are not — those approach the value of the machine.
The advantage of a desktop over a laptop is that almost everything is replaceable. The disadvantage is that sellers know this, so the price often assumes everything works. Testing is how you find out whether it does.
Sources: Microsoft — Task Manager performance monitoring · MDN — Screen API
Frequently asked questions
What should I check first on a used desktop?
The monitor, if one is included — it is the most expensive single thing to replace and the fastest to test. Run a full-screen dead pixel test before anything else.
Can I check the specifications are genuine?
Open Task Manager on Windows and look at the Performance tab, which reports the real CPU, RAM and GPU. Do not rely on a sticker on the case — those often describe the original build rather than the current parts.
Why does the machine need to boot from cold?
A desktop that is already running when you arrive hides boot faults, which are among the most common problems on older machines. Ask to see it start from off.
Is dust inside the case a dealbreaker?
No, dust is cleanable. But a heavy build-up tells you the machine ran hot for a long time, which matters for the components' remaining life. Treat it as a negotiating point.
What do bulging capacitors mean?
Small cylinders on the motherboard with domed or leaking tops indicate a board near the end of its life. That is a repair approaching the value of the machine — walk away.
Do these tests need anything installed?
No. The screen, keyboard, mouse and audio tests all run in the browser on the machine you are inspecting, with nothing uploaded and no account needed.