This just started to occur this morning, the internal speakers work fine, the correct peripheral is selected in Sound>System Prefs (albeit being recognised as 'Digital Out'). The sound slider is greyed out in the menu bar. What is wrong? And can I, myself, fix it (preferably without taking it apart)? I am running a 2011 iMac, bought directly from Apple and only a few months old. There is no red light emitting from my Headphone jack when the ear pods are unplugged. I am running Lion. Thanks!