After a screen replacement, the LCD wont turn on when powered up.

The LCD on my tablet was smashed but still functional, it would still show a picture but due to the damage it wasn't useable.

I bought a replacement screen, and followed a guide to replace it, which was pretty simple but the new LCD didn't work. When powered up it just stayed black, so I bought another screen incase the fault was the replacement part but I'm getting the same behaviour.

If I connect the tablet to my PC, I hear the device connected sound so I know it's on, and it's recognised as Samsung S6 Lite.

I've double checked the connections and it looks ok, so I removed the plastic shield incase the LCD connector on the motherboard was loose but it wasn't. Just to be safe I reseated it anyway.

It's pretty unlikely that I got two bad screens as replacements, so I'm certain that I've done something stupid at somepoint but I honestly can't think what it is. I'm not a professional electronic repairman so I don't know what to look for, or even where the fault might be.

I've attached a photo of the dissasembled tablet in the hopes that someone might spot what's wrong.