You May need to reinstall the operating system, but im guessing your having bad incompatible startup software install try doing this first.
Shut down your Mac and wait 10 seconds.
Press the power button.
Immediately after you hear the startup tone, hold down the Shift key.
You should press the Shift key as soon as possible after you hear the startup tone, but not before.
Release the Shift key when you see the gray Apple logo and progress indicator (spinning gear).
Go To System Preferences> Users & Groups >Click on Your Admin Account > Click Login items> Click The Lock On The Bottom To Make Changes> Click The Minus To Delete All Login Items. If You Cant Access This Tru Safe Mode You Will Need To Reinstall The Operating System Again.
To leave safe mode, restart the computer normally without holding down any keys during startup.
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