Is it just L4D2 or other games? If it's just Left 4 Dead 2, try uninstalling it from Steam then re-installing it. If that doesn't work, then uninstall Steam completely and re-install it and your games. One of these should fix your game.Right, so L4D2 keeps crashing and shutting down my monitor (i'm thinking the video card stop transmiting)... i'd say it';s a heat thing, but even with everything on medium it still does it and other games don't do anything no matter how much i play them... doe sValve just hate 8800's?!
If it's ALL your games, then yeah, it's probably a hardware issue and your boned.