MacBook Pro completely dead after display replacement

I had two broken MacBooks. One worked fine, except the display was broken. (tested on external monitor)

I just swapped a working display onto the Macbook. After replacing it the Mac is completely dead. Won't turn on, no Apple ding. Nothing.

I unplugged the battery during replacement just to be positive I couldn't short anything. No possible ideas what could have happened, but this is super depressing. What do you guys think.