Screen is black after replacement

I followed the iFixit guide to replace the screen. Initially the phone battery was fully drained. I removed the old broken display, connected the new one, charged the phone a little to test if the new screen is working and glued it. However, I didn't to a good job with the glueing and decided to take the screen off and reglue it without disconnecting from the motherboard. I didn't remove the battery either which was charged at about 20% at that point.

Now the screen is black and I can't see any apparent damage to the connector or pins.