@9b033548 Have you tried Safe Mode? Hold down the shift key immediately after boot. If that doesn’t work, try Recovery Mode and run Disk Utility on the drive.
@dff99b33 I tried this.. but it didn’t seem to work, and I wonder if that is because I have a wireless (Bluetooth) keyboard? Do I need to go pull out my wired keyboard?
@9b033548 Here’s the shortcut page from Apple: https://support.apple.com/en-mide/102603