It sounds like one of the column's might be muted.
Try opening the terminal and run:
Raise all of the columns all the way up. Mute and un-mute each column if need be-
Do a sound test which is file "noise.wav
At the bottom of each column you'll see something like 
which means un-muted and [mm]
of course is muted.
You can also try opening the mixer and raise up the pcm and the master,
Adding yourself to the audio group log out and log back in again.
Make sure that you have the Linux Sound Architecture Driver
The file if you want to check in on it I think is in /etc/init.d/alsa-utils or
Hope that helps-