It sounds like a hardware issue. If it was not, then it would work on the next reboot.
I don't know if this is an XP issue, video card, or driver issue. I just recently got XP SP3 working, then windows updates, then Norton, then a video card driver update. Then after a 24hr download of a game through Steam, I started getting periods of flickering then not vertical lines and black screens and sometimes an RaUI program page. I'm not sure what to do next. Any ideas?