1. do you have permission to access it? (ls -l /dev/dsp). Are you trying to use it as a normal user?
if you *dont* have permission then look at the group. if it's root, the chgrp it to 'audio'. then make yourself a member of that group.
(eg: ls -l /dev/dsp, if it says "root audio" that's fine. if it says 'root root' then do 'groupadd audio' then 'chgrp audio /dev/dsp'.
then 'groups <your username>', then 'usermod -G list,each,group,you,are,currently,member,of,and,then,audio <username>'
then you need to logout and log back in for the group changes to take effect.)
2. Is the volume turned up? is the card muted? it can often default to mute all devices. open your mixer program and check the volume levels...
that's a start