Sound decided not to work anymore

The audio on my powerbook just inexplicably and suddenly stopped playing; I've checked every volume control I know of, tried headphones, repaired permissions, and it still will not make a sound. Help!!! Are there any hidden 'mute' switches in OS X I might have tripped on accident? Or is my sound card screwed up?

EDIT: I just plugged in my USB-> headphone adapter, and sound is fine.... I hope it's not hardware, but it seems to be that way.....

Well it seems to be working now... I guess...