same problem as it seems several people here have had: greyed out mute in sound prefs. i've jiggled headphones in and out (which worked once before it ceased working), reset the pram, all to no avail. I've found several threads on this issue: http://forums.macrumors.com/showthread.php?t=683430 Which lead me to check Audio in System Profiler to discover this: "Audio ID = 0" and nothing else. Some people have speculated that this is a motherboard issue, rather than just a cable or sound card problem. Is that true? Also, never had a motherboard replaced on my computer. Luckily I'm still under AppleCare. Can anyone clue me in on what I'm in for here in terms of time and any pitfalls/issues to look out for? Muchas gracias.