Did you disconnect the battery when working inside? If you din't, then there's a very high chance you'll short components like resistors and fry something that is critical for a phone to work, like the chips that controls the output on the screen.[br]
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If you did disconnect the battery, however, I have no idea why the screen won't work - never encountered that issue. However, I did have the same problem as you on the matter of the Face ID on an iPhone X. I took it apart, tried to replace the whole casing, did everything perfectly and carefully, and when I reassembled it the Face ID just crapped out. That thing is seriously delicate and fragile. [br]
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In your case though, it's probably the proximity sensor. The phone relies on it to measure the distance of your face to the Face ID module to get an accurate reading, and if you did tore the cables then that could be why Face ID won't work, and not a problem with the Face ID module itself. [br]
As to the screen, I'm not sure what the issue is. Maybe you should clean the press connectors or check both screens' flex cable for tears or cuts. I still have no clue what the issue is after looking through the internet. If you reconnected the screen when it's powered on though, then it won't work; you'll have to restart it. [br]
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Hope this helps!