Dust and debris could keep your phone from charging properly. ... Wait until the batteries die completely and the phone shuts down and then recharge the phone, and restart it after it's fully charged. If there is a critical system error causing the black screen, this should get your phone working again.
It depends on what you mean by Black Screen. If there is no Display then I believe that it would be a Hardware Problem. If you mean that the Screen is Black but the Phone is On then it could be a Software Problem. I would suggest that you try to Flash the Firmware of the Device to a different Region.