Screen black after replacing, same with old screen (sometimes)

When I connected the new screen it was black and didn't display anything although the phone is working otherwise. Then I connected the old screen and that didn't work either, so I looked up what could be causing the problem and found it might be the proximity sensor making the screen stay off, so I removed the sensor gasket and then my old screen worked, but then I tried the new screen and it still didn't work, and now I can't get the old screen to work either, so I'm at a bit of a loss now. It seems like when I connect a new screen I may have to reboot in a certain way to make it come on but it's difficult to be sure what's the reason it's not working each time I try.