This sounds like either a bad SSD or one that has a bad OS install.
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This sounds like either a bad SSD [https://www.ifixit.com/Guide/MacBook+Pro+15-Inch+Retina+Display+Mid+2012+SSD+Replacement/9706].
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Do you have an external drive which you can setup as a bootable drive from another mac system (make sure you are using the same macOS release)
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Or, has a bad OS install, do you have an external drive which you can setup as a bootable drive from another mac system (make sure you are using the same macOS release)
This sounds like either a bad SSD or one that has a bad OS install.
Do you have an external drive which you can setup as a bootable drive from another mac system (make sure you are using the same macOS release)