Comment 22 for bug 156580

I've had similar problems with the Intel HDA, especially in Hardy.

First check to make sure all Amplifier/Auxiallary is shut off. (gnome-alsamixer).
Then restart alsa (ctrl+alt+backspace afterwards).
If audio is still missing, this is what I did.

For some reason in hardy the sound will just quit on me. Especially after watching youtube videos.
 I killed the PulseAudio in the processes (it was eating ~50% of my processor). And it worked automatically.

I hope this helps someone. And hopefully there'll be a fix. Unfortunately,when this happens, it doesn't trigger the bug report tool. When/if it happens again, I'll file a full report with my methods and results.

-Shoe