Cant change sound volume

Hey all,

I'm attempting to change the volume on my macbook pro, but it doesn't respond to the volume control, and when I attempt to open sound up in system prefs, it just freezes that app. I have to kill it. Sound works, and I can change the volume in iTunes, just not using the keyboard control for volume, or via sys prefs. Any ideas? Opening about this mac also does nothing, strangely. I'm on 10.5.

Cheers,
Marc