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.
To start your mac in safe mode, start with the mac turned off. Press power then *immediately* press and hold the left shift key on the keyboard. Keep holding it till you hear the startup chime, then release. That should start you in safe mode.
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 .
Let me know if you get stuck or cannot shut down the mac to perform these steps.
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