Have you tried a different LCD and LCD cable? I'd start there. You said the lcd was never disconnected? I guess that means there isn't glass shards stuck down in the connector (i've seen that a couple times)
If you've tried the lcd and lcd cable, next I'd start chasing on the board looking for something damaged. If you've got a microscope it'd be super handy for this. I'd suspect you're looking for physical damage, tool damage of some sort.