[AC Question]

when i do call my screen become dark and the same when somebody call me during 1 second the screen become dark and no come back. i cannot use anything symbols like end call, speaker and others. i have to do power off and on to start to do new call.

[B. Diddy]

Welcome to Android Central! Which phone? It sounds like the proximity sensor is malfunctioning, or might be blocked by something. Make sure it isn't obscured by a dirty screen protector, or an ill-fitting case, or your finger. The sensor is usually right next to the front-facing camera.