It sounds like your battery has so little charge that when you try to power on something of a high current draw nature (such as a light) it takes the power away from everything else in an attempt to power on what you are trying to use. I would check that switch and make sure that the uncovered connection is not touching any ground point, and then charge your battery and try to start the car again. It sounds like you most likely blew a fuse when the switch connection initially hit the screw (typically happens when a positive lead is accidentally grounded), so if the aforementioned doesn't work then I would check all fuses with a meter (check for resistance between two fuse terminals, should read close to 0). Once that is done and faulty fuses are replaced if necessary, then it should work again. Let me know if that works.