Hi, welcome to justanswer.com! My name is Mike.I am going over your question and I will be with you shortly.
OK restart and hold the Shift key until you see the Apple logo. If you can't restart from the Apple menu hold the power button for 10 seonds to shut down, then start it up and hold the Shift key... This will activate Safe boot and it will check the drive for errors among other things. It may take longer to boot and you may see a progress bar during part of the process. If it starts up OK, login then restart the normal way from the Apple Menu. Let me know after.
What year and model Mac is it?
1. Shut down the computer.
2. Plug in the power adapter to a power source, connecting it to the Mac if its not already connected.
3. On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time, if it starts up you held the power button before the other keys, try again.
4. Release all the keys and the power but
ton at the same time.
5. Press the power button to turn on the computer.
6. Press and hold the Command-Option-P-R keys before the gray screen appears. (You have to do it pretty fast if you miss it just shut down by holding the power button for 10 seconds then start it up and continue with step 6).
7. Hold the keys down until the computer restarts again at least twice.
8. Release the keys.
Did you try that?
Are you sure it is shut down do you hear the startup chime when it starts?
Did you hold the power button for at least 10 seconds first?
Do you still need help? You never replied.
Black Screen Issue:
Hold the power button for 10 seconds then start it up and hold Command and S keys, to get you into the single-user mode.)
You then need to type the following commands:
You will have to press the Enter/Return key after each one. The fifth command restarts your Mac. It will show the login screen. That's normal, even if you previously bypassed it. Type in your password ***** let me know after.
Ok If you are satisfied, please kindly provide an OK or Above Rating - so I get paid. Keep in mind you can always come back to this page at any time regarding this question for no extra charge. Thanks!!