My sound randomly stopped working. My Macbook Pro's sound emblem does not let me drag the sound up or down. Also, when I use the F10, F11, or F12 keys the regular audio clip comes up but with a "Do not enter" sign below it. The odd thing is I hear the starting chime when my Macbook pro starts up. I've heard people suggest something with a red light in the headphone jack, but I have no idea where this red light is supposed to be visual. I usually run my audio through speakers but those don't work either. Everything with sound in my System Preferences says no input or output devices found... WHAT IS GOING ON?