iPhone 6 LCD screen is black even with a new one.

I have an iphone 6. I replaced the screen with a new one and now the screen is black. It powers on when I recycle the battery cable (disconnect battery cable and reconnect) but after 10 seconds it goes black again. I can hear sounds from the phone but the screen is black. I tried the screen on another iphone and it works fine.

The motherboard/logicboard also gets hot in the first few minutes when I test the phone. There is no water damage. What could be the problem here. Would appreciate anybody's input. Thanks