[Phanman]

Friend had this problem a few weeks ago...

I doubt its your video card as stated above. Its probably a registry issue or software issue caused by a virus.

Start the computer with the windows CD
select R for repair, then at the prompt type chkdsk/s
once its complete you will probably have to type chkdsk/r (repair)
and exit once finished

If that doesnt work try:
boot with windows CD
select R for repair
at the prompt type bootcfg /rebuild
when it says Add installation to boot list? Press Y
then it will say Enter Load Identifier type windows xp (or your version)
then it will say Enter OS load options: type /fastdetect
once complete take the disk out and type exit

Give it a try and see how it goes. If everything does work out, then I would download AVG (free antivirus) and Search and Destroy (free spyware). If you do have virus I would run it twice for each. Also download reg seeker to clean up your registry.

Hope it helps,