I might have a solution for you, but you won't like it. I was recently working on my computer when I thought I pulled out a small cable that runs to the front audio ports on my case. It was a ground, and it turned out it wasn't supposed to be plugged back in

. Booted up and no more audio. Blew something in there that controls it. Needless to say I had a few choice words.
Then after a trip to Fry's, picked up a cheap $15 pci sound card. Plugged it in, installed the software with it, works great again.
Moral of the story, if you don't know where a cable goes, don't bother plugging it in. And after the onboard sound was blown it was still showing up ready to output on my computer just nothing came out.