Computers have a million ways of going wrong. Even if you have used one for years, you may be caught out by some trivial problem seeming worse than it is. We were once called all the way from Brighton to London to find out for a College Principal that the fuse in the mains plug for one of his new computers had blown. Don't be over-awed by the complexity of the machine into thinking that matters are worse than they are.
1. First of all, unplug the computer from the mains, or switch off any switch at the back of the case. Modern computers keep the power on inside the case, even when the front switch is off. That sometimes means that the computer does not re-set itself properly after an error. A few seconds with the mains fully off may put it right.
2. Do any lights at all come on? If not, check the cable and fuse. Often the easiest way to check the fuse is to exchange the printer or monitor lead for the computer lead. If nothing at all is happening when your cables are securely seated and the fuse is OK, you may have a failed power supply (PSU) or other component failure.
3. If there are lights, are there any disk noises or bleeps? Some bleeps relate to particular problems with certain makes of computers, so if you get a pattern, like one long and three short bleeps, or if you get a continuous bleeping, make a note of it and mention it on the phone.
4. Does the display start up on the monitor? If everything sounds normal but there is no image at all, check the monitor cables to the mains and the computer. If all is well with these but nothing appears on the screen, you may have a failed graphics card or a failed monitor. Try another monitor if you can. If you have a laptop that outputs to an external screen, test the monitor with that.
5. If the first images appear on the screen but the computer doesn't start Windows, then probably either Windows or the hard disk drive has a problem. Note exactly any message you get. Hard disk drives can go wrong at any time; but typically a modern drive may begin to have bad sectors at about 4 years old because the magnetism on the coating is not as good as it was. Often such failures are intermittent at first, and the machine may start on a second or third try. Get it looked at, though, and back up your data. Don't assume all is now well.
6. Windows may have a corrupted driver or a faulty file that stops it going into normal mode. Press the F8 key repeatedly (about once a second) while the machine is starting, and select 'Safe Mode' from the start menu when it appears. If it takes you into Safe Mode, that may help you to find out what is wrong. If you just loaded a new program or changed a setting, try going back. With Windows XP, 'Safe Mode With Networking' may allow you to access the Internet if you are on broadband, though probably not if your broadband modem is a USB type.
7. If none of the above has helped, and assuming that you have tried to re-start several times in Normal mode, then you probably need professional help. In the Brighton telephone area you can call Flying Disk-Doctor. We do sometimes go further afield, but that is not really economic unless you have a major job like a network to sort out.