My stepfather downloaded the windows updates, one of which was the "Genuine Windows" download. He's been told he has got a pirate copy of windows. I suspect this is not true (we've all heard of the issue with the "Genuine Windows" update. He was offered more updates through the auto-updater, and they were installed. Windows required him to re-start, yet now the computer will not boot up. It goes to the black screen, tells us his processor type, and then nothing happens

Can anyone suggest what is wrong? If needed I can try to find more information, but it's difficult, as it refuses to do anything

Try booting into Safe Mode options:

After the power-on and BIOS POST or your Logo screen repeatedly tap the F8 key or hold the Ctrl key before Windows starts.

If you get the options page try: Last Known Good Configuration.

If that doesn't work boot the XP CD and run a Repair Install as seen here:

How to perform an in-place upgrade (reinstallation) of Windows XP