sound will only come from one source?

[franze3]

I've been having this problem for a while. Whenever I'm watching a video or playing a game I can't get audio to work for any other program. For example when I have a game open and its minimized itunes won't ever play a song and I get no audio from Youtube. Or if I'm watching a video on one site, I won't get audio from another site even if the video isn't playing. Any ideas what could be causing this? thanks for the help