Possible Duplicate:

My sound stopped working today, how can I fix it?

I'm baffled by this discrepancy:

1. This speaker test is successful:

   
   
   

   speaker-test -c 6 -D 'surround51:CARD=PCH,DEV=0'
   
   




2. Sound Settings is behaving as if I have no sound card:

   
   
   

   

How do I find out what's causing this problem?

Details

Have a look at aplay -L, pacmd list-cards, lshw, pulseaudio -vvvv, and pavucontrol. I do not use HDMI.

This discussion of a similar problem on a PulseAudio mailing list suggests that changes to /etc/pulse/default.pa might be responsible, but I have not edited this file.