Sound Problems

[w4rl0ck9]

Hey I'm kind of new here so this is my first post.:) I'm getting this problem with my computer where I will go to play Call of Duty World at War and the sound will mute, then I have to ALT+Tab out and unmute and it will work fine but then when I exit the game, the sound will mute again. I dont know why this happens.

http://www.worldstart.com/tips/screenshots/Volume-Control-Wave-Mute.gif