Most likely, the display cable was slightly disconnected, when the unit was dropped. You should be able to fix it just by opening it, and re-attatching the cable. I'm assuming that it's an iPad 1 (Not an iPad 2) so you should be able to use this guide to open it and access the display ribbon cable.
Once you open it, disconnect, than re-connect the LCD cable (Surrounded in a yellow box, shown in this picture)
I just dropped mine about five minutes ago and all I did was smack the bottom right corner on my knee one good time and it seemed to pop it back into place. There are a few pixels that are still fuzzy, but it isn't bad at all. Not very noticeable either. I probably will have it fixed later though, just to be safe.