Doesn't turn on with a good battery

Hello all,

I have a 2nd gen nexus 7 that won't power on. I first thought that maybe it was just a dead battery and bad charging port, so I soldered in a new charging port. No dice. I then took the charged battery out of another working nexus 7 and popped it in. Still not starting.

I of course tried holding the power button down for a long time and to try and boot it into the bootloader/recovery screen. Nothing.

The only other thing I've tried so far is switching the silver ribbon cable from the nexus that works, and that didn't work either.

I can see that the motherboard has been taken out at some point because the seal on the screw was chewed up, however the seal on the daughterboard was fine (could've still been removed and replaced carefully). I don't really know where to take it from here.

I can do SMD soldering if that helps.