Sound problem

Hey everybody.
I have a little bit of a problem with my MBP.
Sound works when i hit F11 and F12, I can hear the sound ticks when the HUD comes up.
Also, everything from iTunes works fine.
I have a 150GB music library, and every song plays just fine.
However, when I try to play audio out of any other program -
Quicktime, Safari, Chrome, Firefox, Garageband, VLC, mplayerX... i get no sound at all.
Youtube videos will play, but without any audio whatsoever.
Quicktime doesn't seem to like this at all and crashes routinley.
Does anybody have a fix for my problem?
My specs are: 13" MPB, 2.3GHz i5, 4GB RAM, Lion 10.7.1
thank you very much!