Alrighty. You should have a removable SSD (Solid State Drive) and you can find out how to remove it here: MacBook Pro 13" Retina Display Late 2012 SSD Replacement
EDIT: Order a NEW logic board and replace it, please look at the iFixit guide for help.
You should buy a SSD to USB 3.0 to plug into another computer and copy your files. After you made sure the backup is secure, put the SSD back in. After that process, install macOS onto a blank USB (I recommend a 32 GB USB) and hold down the option key. You should see an option with a USB icon. Click the USB drive and then hit the arrow. If you get to the installation screen and it does not give you an option to install off of the SSD, go into Disk Utility and erase the SSD. Double check you have your files copied to your other PC. For the new drive name, I would choose "Macintosh HD". It should install, but make sure you keep the USB drive into your MBP until you are sure the setup is fully finished! (being able to go onto the desktop screen, and you can see your finder icons.)
After you get macOS installed, take the USB out and format the USB with the PC you copied your files with. Then, drag all of the files onto the USB in the file viewer (could be Finder or Explorer) and wait for them to fully copy. Safely eject them by finding the eject icon (⏏) and plug them into your MBP. Copy the files to your MBP and keep the USB drive in a safe place for a backup.
I really hope this helps!!
crwdns2934105:0crwdne2934105:0
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crwdns2915270:0crwdne2915270:0
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crwdns2944067:02crwdne2944067:0
Hey guys - both of these sound like great ideas. This is an 11 yo machine so I’m not super worried about bringing it fully back to life (tho I love it so). I just got a M2 MBA yesterday, and would love to transfer what wasn’t backed up to this new machine. Sounds like both Dan and diss are suggesting options that involve me removing the ssd and installing it into this envoy which seems doable (and cheap). Do I need to do the full solution with the OS installing if I just put the ssd into the envoy and plug that into the new machine? Any videos you can refer me to of course a huge help.
And THANK YOU for your timely responses and details thus far. Was of course told I was dead in the water by all of the AASP’s and Apple themselves.
crwdns2934271:0crwdnd2934271:0 Max crwdne2934271:0
@max52484 - No need to reinstall the OS as your not running the external drive (using the Envoy case to hold your SSD)
As your now running, I would backup your stuff or use Target Disk Mode to transfer your stuff to your new system.
crwdns2934271:0crwdnd2934271:0 Dan crwdne2934271:0