Hardware troubleshooting: find the fault

These checks need no tools and work on any make of laptop or desktop, whatever system it runs. They will not fix every fault, but they tell you which part is to blame, and that is half the repair.

Safety first

• Unplug the charger or mains lead before opening anything.
• Never open a power supply or a charger: they hold a dangerous charge long after they are unplugged.
• A swollen laptop battery can catch fire. Stop using the machine, do not charge it, and do not press on it.

It will not switch on

1. Try another wall socket, and check the charger's own light if it has one.
2. Laptop: unplug the charger, hold the power button for 30 seconds, plug the charger back in and try again.
3. Desktop: check the switch on the back of the power supply and reseat the mains lead at both ends.
4. Disconnect every USB device, dock and memory card, then try once more.

No lights and no fan noise at all usually means the charger, power supply or motherboard.

It switches on but the screen stays black

1. Turn the brightness up, and listen: fans or start-up sounds mean the computer is running.
2. Shine a torch across the screen at an angle. A faint picture means the backlight has failed, not the computer.
3. Connect an external monitor or TV. A good picture there points to the laptop screen or its cable.
4. Desktop: count any beeps and look for a small code display or coloured lights on the motherboard. The pattern identifies the failing part.

It gets hot, loud, or shuts down

1. Use it on a hard, flat surface. A bed or sofa blocks the air intakes.
2. With the power off, blow the vents clear with short bursts of compressed air.
3. If it still shuts down under load, the cooling system needs cleaning inside and new thermal paste.

The drive clicks or files go missing

Switch off. Do not run repair tools, do not keep restarting, and do not put the drive in a freezer. Every extra minute of running can damage the surface that holds your data. If the files matter, this is the moment to ask about data recovery.

Liquid spill

1. Switch off at once by holding the power button, and unplug the charger.
2. Stand a laptop open and upside down, like a tent, so liquid drains away from the keyboard.
3. Do not use a hairdryer and do not rely on rice.
4. Do not switch it on to see whether it works. Corrosion starts within hours; a clean inside the first day or two saves most machines.

The battery will not charge

1. Try the charger in another socket and check the plug and cable for damage.
2. Look into the charging port with a torch; fluff packs in over time, especially in USB-C ports.
3. Check battery health: on a Mac, System Settings, Battery; on Windows, run powercfg /batteryreport in Terminal.

Random freezes and restarts

1. Run a memory test: mdsched on Windows, Apple Diagnostics on a Mac, or the memory test in the Linux start-up menu.
2. Note whether it happens when the machine is hot or under load (cooling), or at any time (memory, drive or power).
3. Desktop with two memory modules: try each one on its own.

When to stop and call us

If the checks point to the motherboard, screen, power circuit or drive, the next step needs tools and parts. Tell us what you found: it shortens the diagnosis. Advice by phone and email is free.