Member Since: Jan 23, 2008
Location: Fort Worth, Texas
Mac Specs: 27" iMac i5, 3.2 GHz, iPad 3, iPhone 5c, 3 iPods, Yosemite
02-14-2012, 01:00 PM
OK, let's reset the System Management Controller (SMC). Do this:
Shut down your iMac. Remove the plug from the AC mains, and let it sit for 5 minutes. Plug it back in and boot up. Check to see if you can now remove the mute from the sound preference panel. If that doesn't work, try a PRAM reset:
Shut down the computer.
Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously.
Turn on the computer.
Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
Hold the keys down until the computer restarts and you hear the startup sound for the second time.
Release the keys.
Let us know.