Help! '12 MBP won't boot | Folder w/ '?' symbol | NOT HDD NOT HDD CABLE FAILURE!


Okay so I've looked and looked over countless forums to not find a similar issue.

I have a mid-2012 MBP a1278 i7 as well as a mid 2012 MBP a1278 i5

Last week the i7 Model froze while I was working on it (though it was common to get hot) and so I had to force reboot it to attempt to refresh the spinning wheel of death.

However upon reboot, well I could not reboot. I know longer could see my HDD in Disk Utility ...only Base OS x that is 2gb storage size?

Now many support staff have suggested its a faulty drive, and when I replaced that they then said it was a faulty hdd cable, but when I replaced that as well...nothing changed.

It was then that I decided I would diagnose with my i5 model a1278 and to my suprise...the HDD booted...a little slower but just fine.

So clearly the hard drive and hard drive cable are not the issues. So then, what happened? The unit wasn't dropped so I don't have any clue on what to diagnose now. It's really frustrating. Any and all help would be appreciated. Thank you.


Move the boot drive from the i5 MBPro to the i7 MBPro.
Does the i7 MBP boot then?

If it does boot with that known-good drive, you DID say that you noticed that it gets hot frequently. An 8-year-old system, getting hot, might be worthwhile to open it up, and replace the thermal paste on the CPU heatsink.
And, try a different hard drive.
Better yet, swap in an SSD. You can install OS X on that SSD from your i5, working system, then swap in the SSD, with the fresh macOS install to your i7.
(If you get no-boot, even with the drive + SATA cable from the working i5, then most likely, it's the drive controller chip on the logic board. Replace the logic board to fix that )