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Try this first. Shut down your Mac, force-ably if needed.
Shut down your Mac.
Locate the following keys on the keyboard: Command (⌘), Option, P, and R.
Turn on your Mac.
Press and hold the Command-Option-P-R keys immediately after you hear the startup sound.
Hold these keys until the computer restarts and you hear the startup sound for a second time.
Release the keys.
Start in safe mode. You will hold down the left shift key on your keyboard as soon as you press
the start key. Will the Mac start in safemode?
If so, run this repair next.
Open your finder ( magnifying glass ) type in disk utility, and launch the disk utility application.
On the left side of the disk utility window, click your mac hd, then at the lower right hand side, click repair permissions .
Get back to me once you have done this.
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