Sound is not working right at all

[patrick_here]

Hello,
I'm running Mint 12 Lisa with xubuntu-desktop (xfce). Some time ago I messed with my sound (between Alsa and Pulse) changing configurations somehow (I don't remember what I did). Now my sound doesn't work properly; when I play a video,for instance, the sound is very muted. If I attempt to raise the volume I get a very loud humming.

If it were possible to somehow return my system to its default configuration I'd like to do that. Or can anyone advise me on how to fix/debug this problem?

Thank you,
Patrick