mep1972 Said:
"how can you be sure your old laptop is cleared. I followed instructions and at the end I got black screen that's flashing a question mark and then at the bottom shows support.apple.com/mac/startup."
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Assuring all is Cleared:
Fix this by stopping the Flashing the Question Mark. Once stopped, boot into Recovery Mode and then view the disk in Disk Utility. Select the drive, and make sure that nothing exists.
Troubleshooting a Mac with a Flashing Folder:
Three Things...
1. Go here: If a Flashing Question Mark Appears when you Start your Mac - Apple Support
II. Mount the Drive:
Boot into Recovery Mode. Then, using Disk Utility, see if the Hard Drive is seem. If it is, then see if you need to click the “Mount’ button for it. Try rebooting once more. If of no success, then click unmount button, and then the mount button. Try rebooting once more.
III. If Neither of the Above Works...
Reinstall the macOS:
Go Here: How to reinstall macOS from macOS Recovery - Apple Support. Important: Be certain to create a backup of your Mac prior to all of this. That way, you can have something to restore from the Mac from, should anything go wrong with the reinstall. Once reinstalled, try this once mor