When the computer is booted up, the screen does not actually display anything, but simply lights up a little (presumably the backlight turning on).
The computer is a Packard Bell, with an Intel Pentium 4 processor, and an NVidia video card.
It came with Windows XP Media Center, as it was designed to take, and has not had any other operating system installed to it.
I know it is not a fault in the screen, as I have tried no less than four different monitors, and none have any other reaction than described above.
I would put more details, but as you can probably gather, I can't actually see or do anything with the PC in order to get them.
If you have any questions, I can try and find an answer to them, but there are no guarantees.
All I am trying to do with this machine is to get it back to factory condition, which would hopefully fix this problem (probably brought about by a virus, as he says he downloads lots of bits and pieces form the internet).
I haven't got long to fix it, so a speedy reply would be greatly appreciated.