iPhone black screen after the repair

Hi all, I was trying to repair my wife's iPhone 11 Pro max which had lines on the screen. I received a second hand screen in good cosmetic condition. It was taken off from another iPhone. I followed the instructions carefully and put the new screen on but the screen only woke up if I pressed the power button many times. Other times only the screen backlight turned up. I left the phone overnight and in the next morning, the screen wouldn't turn on at all. I thought the new screen was faulty so I returned the original scrren but had no luck. The phone itself is still functioning though apart from the black screen. Any thoughts? Thanks in advance.