If your Mac starts up to a question mark
A folder with a flashing question mark means that your computer's startup disk is no longer available or doesn't contain a working Mac operating system.
While in Recovery, use Disk Utility to repair your startup disk. Then proceed based on the results:
If Disk Utility finds no errors or repairs all errors, restart your Mac by choosing Apple menu > Restart. If the question mark returns after restarting, start up from Recovery again, then reinstall macOS from Recovery.
If Disk Utility finds errors that it can't repair, use Disk Utility to erase (format) the disk. Then reinstall macOS from Recovery.
If your startup disk doesn't appear in Disk Utility, or Disk Utility reports that the erase process failed, your Mac or startup disk might need service. Shut down your Mac and unplug all nonessential devices, then try once more. If your startup disk is an external storage device, check its cable, connections, and power as well.
If the question mark appears only briefly before your Mac starts up normally, make sure that your startup disk is selected in Startup Disk settings. If that doesn't help, reset NVRAM and check the setting again.
