iTunes and audio won't play

I just did the iTunes upgrade earlier today and iTunes was working after that. But I did a restart, was in Windows for a little while, came back, listened to music, went back to Windows, then came back again to OSX, and now my sound will not work at all. iTunes won't even play, even though it says it is but the status bar does not move. Also, there's absolutely no sound coming out of my speakers when i increase or decrease the volume. I tried using the internal and external Boses i have, nothing. What could be the problem?

If GarageBand is installed, launch it and see if it will reload the audio kexts.