Q:

Sound Settings is missing all output devices

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

I'm baffled by this discrepancy:

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

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. 

A:

Turns out I was running into Bug #590780: Installing "randomsound" package causes Pulseaudio to stop functioning at reboot and didn't know it yet.  See this answer:

Run pstree | less
In that, type /arecord and press return to find the arecord process. 
Press up once and you'll see its parent.  In my case this was randomsound.