macOS Sierra: Start up in safe mode
Starting up in safe mode may help you diagnose problems you’re having with your Mac.
Note: To print these instructions before you start, click the Share button in the Help window, then choose Print.
Choose Apple menu > Shut Down.
After your Mac shuts down, wait 10 seconds, then press the power button.
Immediately after your Mac starts (some Mac computers play a startup sound), press and hold the Shift key.
Release the Shift key when you see the gray Apple logo and progress indicator.
To leave safe mode, restart your Mac again, but don’t press and hold any keys during startup.