If your new installation of Ubuntu 12.10 is has no sound or seems to be permanently muted the following may help.
Open Alsamixer by running this command in the terminal(Ctrl+Alt+t):
Check to see if 'Auto-Mute Mode' is set to 'Enabled' as in the image below, if it is move on the next step to disable it.
Navigate to 'Auto-Mute Mode' with the right arrow key.
Set 'Auto-Mute Mode' to 'Disabled' with the down arrow key.
Hopefully you will now have your sound working correctly.