I've had this problem with other Debian based distros.
My current distro is Mint 13 xfce 64-bit.
I have a HDA ATI SB (Alsa mixer).
Here is how I've solved my sound problem.
On your desktop left click the sound your sound icon.
This should bring up a small window with the words
"Sound Settings" at the bottom.
Left click on Sound Settings.
This should bring up your Sound Mixer.
On my Sound Mixer I have a "Select Controls"
box at the bottom. Click on it.
Select the Controls you require and Close.
Adjust the Controls.
You should now have sound.
You might want to try this with the live CD
and compare with HD install.
If this corrects your issue, please edit your question as [SOLVED]
Wirth's law - Software is getting slower more rapidly than hardware becomes faster.