4. Boot into Safe Mode
Sometimes a black display is the result of corrupt information on the startup disk. You can force your Mac to run diagnostics on the disk by booting into safe mode.
To start up in safe mode, power up or restart your Mac and hold the Shift key until the Apple logo appears on the screen. At that point, let go of the Shift key and let the system start up. It will take longer than normal because it’s running diagnostics during the boot sequence.
After it finishes starting up, restart again to leave safe mode and start normally to see if the black display problem is fixed.