Having a bit of a problem with my iMac. Occasionally i will turn on my imac and i wont have any sound. When i try to turn up or down the sound, there is a RESTRICTION symbol in the sound box that pops up and nothing will happen. The old restart usually works. However, when i try to plug in headphones or an external audio cable, nothing changes. I still get sound out of the computer, and it works like there is nothing in the jack. Ive researched this a lot and i havent gotten any help. All software is up to date, i reset PRAM and did the "unplug everything" drill. Still no change. When i did the unplug everything, its almost notorious for having the first problem of "no sound" Any and all help would be appreciated. Thanks in advance!