Maybe it is stuck in "headphone mode" where it thinks there's a audio cable still plugged in. use a head phone cable to push in and pull out rapidly until the problem is fixed. this is a common problem with my palm pre. works every time after i do this for a while.
most likely the hdd is now broken.... you can always take ur mac to the mac gallery the is near you and have them check it out.....they will do it for free.....when you know what's wrong you can come back here...