Hey guys. I've had this problem for some time now. Sometimes, when I turn on my Mac, the audio is simply not working. In the menu bar, it just whos a grey icon, and when I try to adjust it with the keyboard, it shows a circle, and I can't adjust the sound. The only fix I have, is restarting the computer a couple of times, then it works. It's really annoying, does anyone have a fix for this? Btw, there is coming no red light out of the audio jack. Also, this has never happened when I use bootcamp windows 7.