Question marked as
Try an SMC reset:
https://support.apple.com/en-us/HT201295
Try starting up in Safe Mode:
Use safe mode to isolate issues with your Mac - Apple Support
If neither of those work boot into Recovery and Reinstall Mac OS. (You may need to use the discs you Mac shipped with originally)
About macOS Recovery - Apple Support
If none of those work make a Genius Bar appointment for a free diagnostic:
