I have a Macbook Pro, and all of a sudden i have no sound what so ever...not coming out of the built in speakers...so i tried to plug in my headphones..and the sound doesnt work either.. i looked under system preferences and under sound and everything looked fine...i have tried playing sound from itunes, videos, cd's the internet and NOTHING is working.. It is like it is on mute..but it is not..PLEASE HELP