Having some problems when starting up games

Hey all,
When I try to run certain games, they would start up, take up the full screen, and stay at the black screen. This mostly happens for games like Left 4 dead, Team fortress2, HL2. I'm running the legit steam games, not pirated versions . I tried updating the graphic card drivers but the same thing happens.
The thing is that this doesn't happen always, and I don't know what is causing it. Does anyone have an idea? How can I fix this?


I'm using:
Windows 7
Radeon X1950Pro

Thanks