You can always try alsaconf in a su root terminal to reset your sound settings for alsa.
Just got back from doing that heh. It worked on a soft boot, then for kicks decided to power down, wait a min., then power back up. Same thing. Something must be conflicting, just need to put my finger on it. I'm starting to wonder with me having a ATI 5700HD if its trying to pick up the sound portion of the card and defaulting to it.