After repair red screen and repetitive reboot.

Hi, I did a repair for a friend. He had it repaired at a shop who left traces of a careless job. I noticed top screw on the shield plate was missing as well. After I repaired it, he called me that his phone kept rebooting, not letting him use his phone. He said this was happening after the other shop repaired it. He said first there was a red screen and then it reboots repetitively. Any idea what is causing this? I have an idea that the front facing camera and proximity sensor were damaged and all we need is to take that off and see if it boots.