Cycling between Apple logo and iTunes logo, not recognized by iTunes

I recently used this phone to salvage a screen for a repair, and am trying to restore it to working order. When I originally opened it up there was only one screw holding in the plate on the logic board connectors.

What happens is it shows a dead battery until plugged in, then it does the standard red battery while charging, then the apple logo shows up. The Apple logo then turns into the iTunes 'restore' screen for a few seconds, then seems to just bootloop between these two until I intervene.

Plugging into my Macbook doesn't seem to do anything but provide a power source to fuel this cycle, there's no iTunes recognition. I can't get it into DFU mode either.

I have a hunch it's something physical, I'm planning on ordering a new battery and a new set of screws for the logic board connectors plate, but in the meantime I'd like to hear some other ideas.

Thank you!