hi
There could be many reasons...you need to eliminate the simple ones and report if you still have issues.
1) Is usb device detected?
run
lsusb
also check your /var/log/messages with root powers.
If no usb device looks like appearing in above....post the output of
and the output should be small so does not need to go in code box.
2) So assuming usb kernel module is loaded....and device is detected
post the output of lsusb...we need to see the ids and you can google these as well
3) Now run a good mixer to unmute and raise the volumes for the playback (output) section.
assuming you run kde.....run kmix
if gnome I think its called gnome-alsamixer
I prefer ...alsamixer....but that runs in a terminal and is a package of alsa-utils