What things can cause the display screen to stop working?

This phone works fine and it used to be my phone YEARS ago until I switched to another when its display screen stopped working. Now years later, I found the phone in one of my drawers tucked away, and thought why not! Lemme try and fix it!!! Lol. So, everything on the phone works fine, buttons light up, sound comes out, all that good stuff.

The thing that doesn't work is the screen. It doesn't display anything, it's basically turned off.

When I did have the phone, I dropped it A LOT so I thought maybe something came loose. I took everything apart and found the connectors were still connected perfectly fine.

So what I'm wondering is what the problem could be. Is it the screen itself? It doesn't have any cracks or any visible damage.

And also, just as general knowledge, I am pretty new to all of this, what are the common causes of a screen not working?