Hey, does your screen happen to look something like this?
If so, it sounds like you have the same problem as Broken pixels came back on my ti 84 plus ce LCD, can this be fixed?. If not, could you please post a picture of what your display looks like? It’ll make it much easier to understand what’s going on.
If you’re lucky, the ribbon cable connecting the LCD to the motherboard may have simply come loose. If you remove the back shell you can try re-setting the ribbon cable. (refer to this guide for help with handling the ribbon cable)
If those don’t work, then I know the display is a GiantPlus GPM1421C0 and the latest display is a GPM1607A1 (it doesn’t matter which one you get since they are interchangeable), unfortunately, I have no idea where you could buy one since I believe TI sources them directly. :(
In order to get a working display, you’ll need to buy a broken TI 84 Plus CE(-t) that still has a working display and salvage the display out of that. Make sure not to buy a TI 84 Plus CSE since the display is NOT compatible with the TI 84 Plus CE(-t).
Just out of curiosity, does RAM resetting or reinstalling the OS help fix your display?