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I had similar issues replacing broken screen on Moto G7 XT1962-1. In my case I didn’t have all the cables attached. First it wouldn’t display anything. The connection from battery was loose. Then I found the screen connector wasn’t all the way down. Then it displayed for 30 seconds or so and then shut off. Turns out there is a little connector wire about 1/4 to 1/3 down the right side of the motherboard that I didn’t see and the wire was under the Mobo. Once I brought it from underneath and connected it, every thing works. Except the screen I an using is a little too small, and I am looking for a genuine Moto G7 screen, because the one I got from EBAY and another from AMAZON are both too small. They fit, but there are gaps an the top and bottom and sides.