No sound: Suggestions?

I was looking at a video on youtube, didn't do anything, all of a sudden the sound goes out. I make sure nothing on youtube is muted and it wasn't. So I right click my "SPEAKERS" icon (I'm wearing headphones) I click SOUND, then I click the SOUND tab, and the "test" icon is greyed out, meaning I can't click it. Anybody have any suggestions how to fix this? I haven't had sound in 3 days and nothings muted.

I had to UNINSTALL sound driver, then REINSTALL it. Problem fixed.