Use GPU-Z to log your cards speeds/temps while you play a game. This will confirm whether your cards temps and fan speed are okay or not.
GPU-Z Video card GPU Information Utility 
Do the games crash with an error code?
Check in Event Viewer>Administrative events for the game crashes. Look for the "faulting module". This may point to a particular driver etc.
Are you using any cracked/no-dvd .exe's? Some cracks will cause plenty of CTD.