Ubuntu and Mint have had sound troubles since version 7 Mint & since 8 Ubuntu.
Uninstall and reinstalled alsamixer have work in the past for me (I have done it only with XFCE, and sometimes I have to set the mixer sound as superuser to keep the setting other wise I have to reset the sound every time I boot into Mint.
I'm currently using Mint Debian edition with Gnome and don't have sound trouble.
Try firing up Xchat that will automatically take you to mintlinux-chat and mintlinux-help channels where you might get better result for your questions.