The LCD has failed or become disconnected which is more likely after a fall.
You will need to heat the screen up under a hairdryer and then using plastic picks or a sharp blade work around the home button area and sides and very carefully lift the screen from the home button are upwards. FOLLOW the instructions on the step by step guide here!
Once pen reseat the connector and then if you still have a black screen hold the power button and home button together for about 20 secs. In fact try the button combo first before anything else.