Weird display issue after replacement

Greetings

Having a bit of a weird issue that I haven’t seen or read about on here before even through a lot of searching.

Was replacinf an iPhone 8 screen + front camera. All went fine, plugged the display in powered up used for a few minutes. I wanted to test the auto brightness so I turned it up to maximum and the screen went black as if the backlight had died.

Restarted the phone now now there’s no display through several tries of reconnecting and cleaning the connectors the display turned up once after a hard Reset but as the phone boots the display fades at once stage it stayed on for over a minute so i don’t think it’s the backlight. I want to add I’ve NEVER connected the lcd with the battery connected.

connect phone to itunes and it’s recognised shows a 0% charge

what I have concluded so far

-probably not the backlight ? As the display wouldn’t suddenly come to life for a bit

-phone somehow has 0% charge and WONT charge I think even plugged in OR it’s charging but shows 0%?

-screen isn’t faulty as I’ve tried another one

so im thinking this is some sort of battery chargin issue ? But I’m not sure if he that would cause a no display issue

any help would be appreciated

thanks