LCD not turning on after screen repair

Okay, so I had a client that I replaced the screen and LCD for. She came back to me because the home button worked but touch id didn't following advice i receive i switch the backplate with a new one. when I connected the LCD to the phone again I turn on the screen and the lcd looked damaged. But I know thats not possible cause the screen was not dropped. So I tried with a different screen. The different screen did not work. I eleminated long screw because I never screwed the protective cover over the FPC connectors before i tested it. And the screen worked before when it was screwed in. iPhone still connects to iTunes and the screen will ocassionally turn on to notifications but not home button or power button. It also continues to show lines and the screen will fade to dark but the phone is not turning off when it fades to dark it is simply going into sleep.