On my brothers PC, I installed a genuine version of windows XP Home about a month ago.

Yesterday he booted it up, logged in as normal and the screen said he needed to validate his copy of windows. So "OK" was clicked, and it said that windows was already validated, and then returned him to the log-on screen.

The computer is now in a circle of doing this and cannot be accessed at all except in safe mode.

Anyone any idea how to sort this out without reinstalling, his constant moaning and nagging is beginning to piss me off