on my lg optimus g why does my screen go black and not come back on when i'm on a phone call

[AC Question]

When I make a phone call on my lg optimus g the sceen goes black and won't come back on while i'm on the phone so i can't use my key pad or hang up or do anything

 

[B. Diddy]

Welcome to Android Central! Make sure nothing is blocking the proximity sensor (which is right by the front-facing camera). An ill-fitting case or a screen protector without a cutout for the sensor could make the sensor think that the phone is still against your ear, and therefore would keep the screen off.