If you could post a picture, that would be ideal.
However, seeing as how this occurred following a drop, it is either a damaged LCD or the connectors have come loose. The first thing to try is to open the phone following this guide. Follow the instructions very carefully and keep track of the screws. They are all different and if you put the wrong one in the wrong place, you will severely damage the logic board.
If that does not solve your problem, then I would replace the screen assembly, which you can find here.