Try cleaning the screw heads with a pionted object. Otherwise you can buy 'damaged screw screwout bits. They work good. Ask a friend or buy a multimeter to check the circut in the switch box to see which one is hot. The black wire is hot if you can see the color of the insulation. You can buy a relativly cheap multimeter at hardware stores. Look in the fuse box and find the fuse for the circut you are working on. Usually there is index showing what fuses are for different circuts. The amperage will be on the fuse. And " ALWAYS BE SURE TO PULL OR SCREW OUT THE FUSE ON THE CIRCUT YOU ARE WORKING ON". BE SAFE.