I was just playing around with the Boxee Beta and it hung. I force quit it, and subsequently tried to play a song in iTunes. It wouldn’t play. I tried playing a new song and took note: the time didn’t move from 0:00, the song information was scrolling at the top, and there was a speaker icon next to the song. Yes, the volume was up. Quitting iTunes and reopening it didn’t fix it (tried a few times).
So, I opened up Activity Monitor and did some quick searches to see if I could find something related to iTunes, Boxee, and Sound. Anyway, there is a process called coreaudiod – the core audio daemon. Force-quit that (requires admin privileges) and boom! iTunes works again.