My device has a black screen, yet is touch responsive

Hello everyone, I was given an Apple Watch Series 4, that had a broken LCD. I had one that was broken for whatever reason and I used the screen for it. Now the device has a black screen all the time, except for: when it's low on charge, when it's charging (turned off), and the apple logo booting up. The touch is responsive but after it boots up, the screen goes black and I can do stuff in it with VoiceOver only. I tried forcing a restart and updating it, and also checking if I had Screen Curtain on.