ok possible things:
Your vidcard drivers or directx somehow got corrupted, for this try reinstalling both of them.
other things:
Possibly the memory on your videocard is overheating not the core but the memory on it or the core once overheated and got a punch. Do other games work ok for you (preferably some graphically intensive ones). Try installing 3dmark or something.
Its most likely some hardware part going awol, so test a bit with other things like 3dmark06 and test if things don't get too hot if problems persist then if still under warranty RMA the parts that cause the issue.