Macbook dropped and screen has dark and light

Check the unit with the external monitor> If the external monitor works fine- it could be an issue with the display of the notebook.

If the External monitor is also not comming up ??? its an issue vedio card/graphics card, some time the vedio/graphics card is a part of system board, If you have accidentall damage protection warranty you are lucky.

the display cable is disconnected
open the MAcbook. you need a little careful with the self locking system. there are fewer screws. once you have opened it, remove the motherboard to view the display cable. remove and plug it again. 
if you dont have proper tools it is highly recommeded  that you take it to nearest service centre or technician