Could be many things. Ribbon cable or connection to inverter board could be loose/disconnected. Or the display cables could have been torqued during the drop, a bad cable or connection definitely could cause those lines. Of course it could also be the LCD screen itself, and then you'll need a full replacement, there's no "fixing" a screen. I think that's the most likely, given a fall down the stairs.
One thing you could do, boot into BIOS mode (or Open Firmware mode for OSX). The combo is Power button + CMD, OPT, "O"and "F." If you boot up in this mode, and still see lines, very good chance its a hardware issue. You will not be able to narrow it down after that without unplugging, inspecting and testing many things, i.e. running continuity tests on cables, looking at your inverter for damage, etc.