There is a lesser known cause which is the proximity sensor next to the front facing camera. When this sensor fails the screen can go blank. I look at the looping charger sound as a separate issue if the proximity sensor is out. Replacing the screen (like a cracked screen that was otherwise working) has preceded the onset of these same symptoms many times. This supports the idea the symptoms can be related to the screen, connectors or possibly some other disturbance to the phone while replacing the screen. I've read about success re-installing a new screen, cleaning the connectors, and the phone came back. Also, taking out the blank screen and testing in a known good phone showed the screen to be OK. This could again support need for re-installing or cleaning the board connectors. There is no single answer. I have a phone in similar condition. I'm going to test with some spares from a friend and see what develops. I'll re-post in a week or two with good or bad results. Best of luck!