It is almost impossible to know the issue based on the information, as so many parts could have been compromised. I would start with getting an amp meter, so you can see if the phone is drawing any power, to try and focus in on what is causing the problem. If the phone is drawing a normal amount of power (around 1 amp), then it would point towards some kind of display issue (bad screen, bad backlight, damaged fpc connector etc), but if it's not drawing any power or minimal power, it would likely be an issue with the board.