I updated my macbook pro, having restarted, my sound doesnt work. itunes wont even play, the seconds wont move. even when i press f5 to turn the sound up - it shows a little circle and bar underneith suggesting its on mute. thus i went to system preferences > sound > output volume. it appears to be on full and mute yet its greyed out and i cant select it... when i deselect Show Volume in Menu Bar, then select again and roll my mouse of the volume icon in the top right it simply disappears... LOL? all i did was update and restart like it asked! wtf...! --- when i open garageband it says that the selected driver isn't available...?