Good mainboard won't boot when swapped to different phone topic

I got a Note 2 from a guy on Craigslist that apparently had died. Wouldn't boot, no lights, but battery did warm up after staying on the charger for a while, so it seemed to be charging. Got another note 2 with a busted screen, but which does boot. Screen is completely shattered with no backlight or image on the screen, but you can hear it fully boot. When I swapped the board from the second phone to the dead one, nothing happens still. No boot. No blue light. Nothing at all. I tried the board I pulled out of the first phone in the shattered phone and it appears to boot. Swap the board that came out of it back and it boots, but nothing happens with either board when I put them into the first phone. I've also swapped the usb boards and they both work in the phone with the shattered screen. I'm stumped! The first phone I got is super clean, and doesn't appear to have any water damage to phone or battery, and my shattered note 2 boots with both batteries. I thought the issue was the well known sudden death issue, but it seems I have a different problem. Any suggestions?