seems very unlikely to be the problem and I'm not sure if it's already been suggested, but have you tried the hotfix linked here?
http://support.microsoft.com/kb/940105
any! wow ermmm, thats truly odd, as orthos runs fine for an hour, but you can't load a game!
Do you have a spare gfx card laying about! Yours might be knackered!
see how long it can run this dribble program forif it cant do it forever, then i'm afraid it does sound a lot like a card failure, if so, you need to start looking at warranties and what not