Pre-Retina 2012 15" MacBook Pro does not load into macOS.

[iQuestionz]

Hi, my MacBook refuses to boot into macOS from an SSD or HDD.

When I power on the MacBook everything works fine, the chime is there and the screen is on. But after a few moments, there is a flashing file with a question mark. Im not sure why this happens. I tried loading the same disk on my other MacBooks, and it works like it's supposed to. But this MacBook doesn't want to work with any disk. I tried booting the MacBook with a macOS Installation USB, and it did load I can access terminal, disk utility, etc. But when trying to boot from a hard drive or SSD, it doesn't.

Any suggestions or ways I can fix this?

 

[redheeler]

Is the disk you're trying to boot from formatted as APFS or HFS+? The 2012 cannot boot from an APFS disk unless it has a newer firmware version installed. The way to fix this is by performing a MacOS High Sierra or later installation on the 2012, it will update the firmware as well.

 

[iQuestionz]

I was trying to boot from Catalina macOS which uses the APFS format. I'll install macOS High Sierra on the SSD rn, and see if it works.