Why is my screen going black within seconds of either recieving a call or making a call

Welcome to Android Central! It's probably due to the proximity sensor thinking that the phone is up against your ear. It's normal for the screen to go to sleep on a call when you have the phone up against your ear, in order to prevent accidental screen touches. But if that's happening without the phone up against your ear, then something else might be causing the proximity sensor to activate. This can be a poorly designed (or dirty) screen protector, or a poorly fitting case -- do you have either?