MacBook Pro can’t find startup folder?
MacBook Pro can’t find startup folder - I think - help! Get this when I turn it on
MacBook Pro 13", 10.13
Question marked as
Hold the option Key when you reboot— see if the Startup Disk Manager will let you select the Macintosh HD.
If no luck—Boot into Recovery (Command R) and from the dropdown menu: Utilities> Disk Utility> run the First Aid on your Macintosh HD. If errors are found and repaired, run again until no errors reported.
Recovery http://support.apple.com/kb/HT4718
if still no luck you can reinstall the macOS on top of your existing macOS from Recovery as well.