Try to boot into Safe Mode according to Start up your Mac in safe mode - Apple Support . If success try to reboot normally.
NOTE: Safe Mode boot can take up to nearly twice as long as a normal boot as it's doing the following;
• Verifies your startup disk and attempts to repair directory issues, if needed
• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)
• Prevents Startup Items and Login Items from opening automatically
• Disables user-installed fonts
• Deletes font caches, kernel cache, and other system cache files
If you still can't boot up boot into the Recovery volume (boot with the Command + R keys held down), select Disk Utility and run First Aid on both volumes. If you get any error messages rerun First Aid until there are none. Then reboot normally.