My computer won't turn on

Most computers that seem dead start again after a power reset, a longer charge or reseating the memory. Work through these steps in order, and stop as soon as it starts.

Step 1: Check the power

1. Charge for at least an hour. A laptop that has sat in storage or transit can be completely flat. Check whether the charging light comes on.
2. Plug straight into a wall socket, not a power board, and test the socket with another device.
3. Check the charger and cable for damage, bent pins or a loose wall lead, and make sure it's the right charger for your model (see Charger doesn't fit or isn't recognised).
4. Unplug everything else: USB drives, docks, printers, SD cards and external monitors. A faulty accessory can stop a computer starting.

Step 2: Do a hard reset (power drain)

This clears leftover charge that can lock up the power circuit.

Step 3: Lights or fans, but a black screen?

• Turn up the brightness with the Fn brightness keys.
• Press Windows + Ctrl + Shift + B to restart the graphics driver. You'll hear a beep if it works.
• On a laptop, connect an external monitor. If that shows a picture, the laptop's screen or its cable is the problem.
• On a desktop, check the monitor cable at both ends and that the monitor is set to the right input.

Step 4: Reseat the memory (desktops)

A memory stick that has worked loose in transit is a common cause of a desktop that powers on but shows nothing, or beeps.

1. Turn off, unplug the power cable, and hold the power button for 10 seconds.
2. Remove the side panel. On Mini and Micro PCs, the top cover slides or unscrews.
3. Touch a bare metal part of the case to discharge static.
4. Open the clips at each end of the memory slot and remove each memory stick.
5. Push each stick firmly back in, straight down, until both clips click shut.
6. Still not starting? Try one stick at a time in the first slot to find a faulty one.

On laptops, memory is usually under the base panel, and on many thin laptops it's built in. If your laptop is within 30 days of delivery, contact us instead of opening it.

Step 5: Reset the BIOS (desktops, advanced)

If a BIOS setting is stopping start-up, remove the small round coin battery on the motherboard for 5 minutes, then refit it. This resets the BIOS to its defaults, so you may need to set the date and time again.

Step 6: Run the built-in diagnostics

If the computer powers on but won't load Windows, the maker's hardware test shows what's failing:

• Dell: press F12 as it starts and choose Diagnostics.
• HP: press Esc repeatedly as it starts, then F2 for HP PC Hardware Diagnostics.
• Lenovo: press F10 as it starts, or F12 and choose Diagnostics.

Note any error code it shows.

Warning lights and beeps

Note the pattern (for example, 3 red then 4 white). Dell, HP and Lenovo publish what each code means on their support sites.