First thing you need to do is find out if the phone charging. You can buy a usb amp meter (very cheap) http://amzn.to/2DXxScM and check if the phone is drawing any amps. Anything between 0.2 to 1amp is good and means the phone is charging as it should. Your problem could be a display issue where the phone is working but not able to display an image or backlight to the screen. This is caused by either a short on the 5.7v rail or the display chesnut ic. You can see a video here that talks about how the 5.7v line works. https://youtu.be/qy7FwDgWvnQ