I seem to inadvertently disabled the sound on my MAC (2GHz intel core duo). When I try to change the volume with the keyboard up comes the "no" icon (circle with a line through it). And on system preferences the "mute" on output volume is checked, but it is "greyed out" so I can't change it.
try launching garage band and quitting. apparently some people have sound difficulties after updating to quicktime 7.1.1
Dave