Blinking file folder with question mark

Hello,

This would occur if you had erased your startup disk. These two articles should be helpful in reinstalling macOS.

If your Mac starts up to a question mark - Apple Support

"If the question mark persists, follow these steps:

1. Press and hold the power button on your Mac for up to 10 seconds, until your Mac turns off.
2. Turn on your Mac and immediately press and hold Command (⌘) and R to start up from macOS Recovery.
3. While in macOS Recovery, use Disk Utility to repair your startup disk.
4. If Disk Utility found no errors or repaired all errors, reinstall macOS.
5. If you still need help, please contact Apple Support."

How to reinstall macOS - Apple Support

"If you just erased your entire startup disk, you might be offered only the macOS that came with your Mac, or the closest version still available."

"After installation is complete, your Mac might restart to a setup assistant. If you're selling, trading in, or giving away your Mac, press Command-Q to quit the assistant without completing setup. Then click Shut Down. When the new owner starts up the Mac, they can use their own information to complete setup."

I hope this helps.

Davros, see Scott’s detailed answer above. As soon as you start up he mac, press and hold down the command and R keys at the same time while the Mac boots up — continue to hold them until you see the Recovery menu. Follow the steps Scott has outlined for you above, so you can reinstall MacOS on that machine.

Welcome to the Apple Support Communities.

What year is your iMac?

Jack

Re: blinking file folder with question mark.

When I turn the computer off and then on again I still have the folder and question mark.

Don't know what to do - stuck!

Thank you, all who help in a myriad of situations. Thank you

T'was great help but unfortunately could not start.