Thank you for posting in the Apple Support Communities. I see you're encountering a blank screen when you try to log in.
If you're unable to restart or shut down using the normal methods, you may need to try a force shut down. You can learn more about this using the steps in the article titled How to turn your Mac on or off .
You may need to press and hold the power button for 20 seconds or so in this case.If your Mac doesn't shut down, try Force Quit to close any apps that aren't responding. If that doesn't work, press and hold the power button until the Mac turns off.
Press and hold the power button to turn off your Mac only if it isn't responding. You'll lose unsaved changes to any documents that you have open.
Once the Mac is off, try booting into safe mode. This will prevent certain items from loading, and it may help you to complete the login. Here's how to Use safe mode to isolate issues with your Mac .
These steps should help you log back in to your Mac.Start up in safe mode
To start up in safe mode:
- Start or restart your Mac, then immediately press and hold the Shift key. The Apple logo appears on your display. If you don't see the Apple logo, learn what to do.
- Release the Shift key when you see the login window. If your startup disk is encrypted with FileVault, you might be asked to log in twice: once to unlock the startup disk, and again to log in to the Finder.
To leave safe mode, restart your Mac without pressing any keys during startup.
Have a great day.