Bootloop after lightning flex cable replacement on an iPhone 8

Hi! I recently replaced my friends iPhone 8 flex cable as the old one no longer worked, the battery still had some juice in it so i could boot. But after replacing the flex cable, it now boot loops. Disconnecting the connector makes the phone boot and connecting the old flex cable makes it boot as well. When the flex cable is connected and holding down the power button brings up nothing on the screen. I’ve already tried two new lighting connectors and they also don’t work. Everything is screwed in correctly and everything is plugged in.

Any help is appreciated :)