The other day, I was attempting to play music from my headphones (using headphone jack) and my bluetooth headphones at the same time. I opened Audio MIDI Setup tried to make it work. Eventually, it froze and now I get the error of the circle with the diagonal line through it anytime I try to change the volume. Also, System Preferences does not work at all, and every other application runs slow and I get the pinwheel very often. When I look at Audio MIDI Setup now it says no audio devices and I cannot play sound. I have tried entering the "sudo killall coreaudiod" command in terminal and restarting my computer using alt+command+p+r. When I try this it makes the classic apple startup noise, but then the sound still does not work. Any idea what is going on? Any suggestions would be appreciated.