Why is my screen black when I'm getting a call?

The screen itself may be damaged and it will need to be removed and replaced. If the screen is only turning black when certain functions are being performed such as answering a call, there may be a problem with the motherboard itself or the communication between the motherboard and screen. Remove the cover and check to see if the screen is cracked or broken, if the connection between the screen and motherboard is loose or disconnected, or the motherboard is physically damaged in one way or another. If you can physically see a damaged part, replace or repair that part and that will fix your problem. Troubleshooting - Screen does not work