I also had sound problems when I first installed Mint. Are you sure you had sound prior to the logging in/out as ROOT? I initially attributed my lack of sound to some random event, but then found out by poking around that I never had sound to begin with. I only had sound when I successfully logged into the system, but no sound at all once I was actually in Mint.
There are a TON of Ubuntu audio problem threads on various forums, which I found made it more difficult to actually zero in on a solution. Here is a link to 2 separate solutions http://forums.linuxmint.com/viewtopic.php?f=49&t=33956&p=198039&hilit=killall+pulseaudio#p198039
I recommend trying the 'quick solution' first, and if that works then try the steps that include a "sudo apt-get purge pulseaudio" command.