Plug your phone into a PC, is it being recognized? If so, did you disconnect the battery first? If you didn't there's a chance one of the filters is gone. Take a strong flashlight and shine at the screen, does anything show up? It's usually the case of backlight not working. If you disconnected the battery first have a look around the screen connectors, you might've knocked off one of the microscopic components off. Next have a look around battery and charger ports for any pry damage.
It's also possible you didn't connect the battery / charge port properly.