boot loop after screen replacement (both old and new screen - no BSOD)

Hi there,

I replaced the screen of my iphone 5s and when testing it before closing the case finally, it's stuck in boot loop (without blue screen, just eternally stuck in apple logo and restarting, can't even turn it off). The same problem persists when I reattach the previously working screen (just the screen and digitiser without the camera, audio components and home button that are transferred to the new screen).

I can get it in DFU mode, but can't update or restore the phone (at some point in the process error 9 appears and stops the process).

I have forgotten to disconnect the battery when replacing the screen. Not sure if replacing the screen and changing the parts without disconnecting the battery might have fried some hardware component in the process or whether there might be a different reason for it getting stuck in boot loop?

I have taken the screws out of the EMI shield and made sure that all the screws with the right length are inserted in the second attempt. Don't think that it's screw damage though as this would result in a blue screen, no?

Any tips what I might be able to do to get it to work again?

Thanks so much for your help,

Janosch