Canon EOS 90D power up sometimes..

I recently replaced the motherboard, topcase and LCD of this camera. For some reason it will only power upp occasionally.. It seems completely random... I take the battery out for a couple of hours and put it back in.. Sometimes it powers up.. Most of the time it doesnt.. The switch for the sdcard is fine and the switch for the battery is disconnected.

What is this sorcery? Can anyone help out?