My volume is locked :| How do you unlock it?

when i press the increase/decrease buttons the volume logo appears like normal but the volume blocks don't move, and this sign appears

http://homepage.mac.com/geerlingguy/blog/media/do_not_sign.gif

I checked my sound settings and i noticed that in my Output, no output devices are found. I normally see my built in speakers (or microphone i forgot). No input devices are found as well.

my mac is an iBook G4

i hope someone can help me because i've been without sound for at least 6 days.

*Moved thread to proper forum - Has nothing to do with suggestions or comments on the forum*