Mac starts up to a question mark what should i do to restore it ?

see here:

https://support.apple.com/en-ca/HT204156

A good idea if they after they tried the natural first part,

the problem may require those second steps. ~ Perhaps

re-install, &/or other; follow through. To check hardware.

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

While the software reinstall may be adequate. Be sure to

have good backups; one of those, a Time Machine on USB.

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