Left 4 dead issue

Hey again, now every time i play for 2-3 minutes i am instantly returned to my desktop whit the game still on. This is getting really frustrating, i am playing on Vista64bit please respond.

so ur saying that ur game minimizes and u return to the desktop?

Yeah

Sort of, it happens in non steam games to ; /

I use Avast, and i noticed that it also happens in Team fortress 2. When i restarted my computer it fixed itself. But before that i tried to play in windowed instead, i noticed that something tried to take me back to the desktop and that the game froze for like a second.