Wow, I thought I saw the same problem, same hardware, same sound card in the General forum, all the same except the user's name. Hmmmmmmmmm
Anyways, could be a hardware problem, or try using a different driver, goto:
http://www.opensound.com
http://www.alsa-project.org
And see if you can't use a different driver to get it to work, if that doesn't work, try another sound card.
Good Luck.