Help!

[Empererred]

Okay so anytime I make or receive a call my screen goes black. Which is fine because it saves power, but then I can't ever get back to the screen once a call is made or received. No matter what I press on the phone nothing happens. I have to press and hold the unlock button twice and then that is the only way. Does anyone know what is going on here? So you guys can understand the frustration when I make a call to AT&T and I need to use the keypad, but obviously I can't because the screen is blank.

I'm getting super frustrated so anything information would be really helpful.