Black screen

I broke my phone and just received a new one from the Geek Squad. Two things. When I make a phone call the screen immediately goes black and won't come back on until I push the on button on the back. Really sucks, hard to end call. Also when it times out I have a really hard time getting the screen to light up again. Some times it takes 8 to 10 times pushing the on button and swiping the screen. Any ideas?

Bill