Comment 83 for bug 63352

Go to the Ubuntu sound problems web site and follow instructions.
http://ubuntuforums.org/showthread.php?t=205449

If that doesn't work, try the following:

sudo apt-get --purge remove linux-sound-base alsa-base alsa-utils alsa-source
sudo apt-get install build-essential linux-headers-$(uname -r) module-assistant alsa-source
sudo dpkg-reconfigure alsa-source
sudo module-assistant a-i alsa-source
reboot