If you have the current graphics card and get a bugcheck when starting a game. You want to check: are all of the power connectors to the graphics card connected. Many modern graphics cards get power from 3 sources:
The graphics slot from the mother board, and 1 or 2 power connectors from the power supply directly to the graphics card. check to make sure they are connected and providing power, and also that if you have two supplemental power connectors make sure they come from two separate sources on the power supply.
The second most common failure is when you run a current graphics card and driver but you have windows 7 installed but have not installed the service pack 1 and its updates. Current graphics drivers require service...