The volume control on my MacBook Pro (running Lion) is not working

All of a sudden I lost the ability to move the volume slider for my MacBook Pro internal speakers. It's permanently set to mute. I can't figure out! Every time I go into System Preferences and click "Sound" I get the spinning beach ball of death and crash out. Every time! Don't know where to go from here. Maybe my problem is bigger than the audio thing, but everything seems relatively ormal aside from this.

If anyone has any insights, I'd really appreciate it!

Thanks