Originally Posted by dmw16
I have a 27" i5 iMac and I've noticed recently that my volume control is greyed out. I can't adjust the volume with the slider or the keyboard and the speaker icon (and the screen notifications are greyed out).
When I plug in headphones they work fine, but when I remove them the icon reverts back to grey.
EDIT: Plugging in headphones then removing them seems to fix it if I leave the headphones in for a little bit first.
If you have time, please create another user account and see if the same thing happens.
If it does, you might have a hardware issue. Just like was previously mentioned, the iMac more than likely thinks something is plugged into headphone jack and you plugging and unplugging a set of headphones fixes it temporarily. Did you have an Apple Store close by?