Ally wont charge or start after reassemble

Hello.

I opened my Ally because the B button was stuck and I wanted to clean it. after that I waited 2 weeks for the PTM7950 cooling pad to arrive. Now I reassembled the Device and it wont charge or power up. Maybe someone can help me. I think it has all connector in the ports, but even when I missed a cable it should charge when the battery is plugged in the mainboard, right?

Edit: My Ally works again. the only thing I did was putting the back cover on it. Is there a sensor that knows if the back cover is mounted or not?