Comment 33 for bug 274124

I have been experiencing a similar if not the same problem.

It seems as though pulseaudio isn't using the soundcard as a sink (where audio goes into), its also worth noting that it still detects my microphone and uses that as a source, which works fine.

Load up paman and take a look at anything related to Sinks. Perhaps this has something to do with the problem.

While frigging around with getting it to work something managed to mute alot of volume controls, so check that occasionally.