If your computer won't start up at all, you may still be able to fix the problem yourself.
1) Check your connections
If you've got a desktop computer, you may be having computer problems because one of the cables inside the machine has become loose, particularly if you've moved your computer around recently. Open up the desktop casing (not the monitor) – you'll probably need a screwdriver. Check that all the cables are firmly pushed into their appropriate sockets.
Laptop loose connections are less likely, but if you've recently installed new memory it's worth making sure that you've firmly connected it.
2) Check your laptop battery's OK
If you're running your laptop off its battery, try plugging it into the mains power – if it starts working it's probably time for a new battery.
3) Start up in safe mode
Try starting up in 'safe mode'. To do this, as soon as you switch on, repeatedly press the F8 key. You will be presented with an on-screen menu. Select 'safe mode' – this should allow you to start up your desktop and in most cases will allow you to investigate further, including running a security scan.
Find a recommended computer repair service on Which? Local
If none of the computer repair solutions above work, it could mean some of your computer hardware is damaged – for example, your hard drive or motherboard. If you're a Which? Computing member, contact the free Which? Computing helpdesk to find our your options - it's relatively easy to install a new hard drive in a desktop, but it's much trickier with most laptops and many require a qualified engineer.
Alternatively, Which? Local lists more than 1,500 computer shops across the UK so you can find a repair service recommended by Which? members