Freeze during boot after repair, strange fan behavior, totally stumped

MacBook Pro 15" Retina Display Mid 2012. Replaced the top case due to a cracked touchpad, repair went fine with one exception: during reassembly, the connector on the underside of the logic board for the MagSafe port wasn't seated all the way (battery would show as Not Charging), so I took it apart again and reseated the MagSafe connector. AC charging now functions normally.

Now, however, no matter what you do on the computer (normal boot, safe mode, recovery, boot from usb, doesn't matter), it freezes and the fans ramp up after a minute or so of being powered on. For example, on normal boot, I can get all the way to the login screen but when I type my password, the progress bar goes about halfway but then stops. Immediately after it stops, the fans start to spin faster and faster and heatsink on the processor gets really hot, as in, I could burn myself. So I turn it off before temperatures get too crazy for too long.

Tried multiple restarts, PRAM/SMC resets. Tried a known good SSD. Internet Recovery. USB boot. No luck. Can't even run AHT/Diagnostics because the machine will get too hot and fans go crazy during memory test (doesn't even get a chance to get to the fan test!). By the way - laptop was functioning normally before repair.

Opened it up again, thinking it has something to do with temperature/fans/whatever. Upon closer examination, I find that one of the fan mounts has detached from the logic board somehow. It's the one circled in orange here:

https://d3nevzfk7ii3be.cloudfront.net/ig...

Basically, the little silver thing that the orange fan screw screws into is no longer attached to the board. There doesn't really seem to be anything crucial below it but I suspect that this is the issue.

Is this causing the problem? If so, can it be repaired? Soldered? Or do I need to shell out for an entire new logic board?

Thank you in advance for any help you can provide. Super stumped on this one.