Why is my phone randomly off after sceen replacement?

Hey, i got a Iphone 5s. Sometimes when I try to open the phone, its just black and the phone is off. If i try to mute/unmute when its black, it does not vibrate. And randomly its back on. What should i do? If I'm doing on the phone, then works out just fine. It is only then that I shall open phone that it happening. and if I listen to music that works out the fine.