sound quit

[gratar]

I have been listening to my tunes stored on my Mac Mini, purchased some new ones from the iTunes store when my Mac quit responding. No warnings. When I finally had to quit through holding down the I/O button and restarted... now I have no sound. The " mute" button is checked and I cannot un-mute it. It shows I have no input devices and no output. What happened? How do I remedy the problem? I NEED my tunes!