2004 Honda Civic seized rotor screw.

Hi there, So I am having a problem with my brakes. I needed new pads and bought some aftermarket drilled rotors to put on. I did the passenger front first, caliper and mount came off no problem, rotor came off and put the new one on, new pads and reassembled everything. On the driver side, I did the same but could only get one rotor screw loose. The other is in there good, I hammered it and sprayed it with lubricant and tapped it some more, I will not budge. I ended up totally mangling the slots of the screw head so now its totally a mess. I put the new pads in and closed it all up, I am driving that way temporarily until I can get it fixed. Obviously my braking feels funny, and the pedal depresses all the way to the floor but I can stop, sort of. So my questions are

A) Why do I hear a grinding sound when I hit the brakes hard? Was there before as well. Because of the semi metallic pads?

B) How do I get that screw out to change my rotor? I am driving with new pads on each front side and one new rotor and one old rotor. I have a friend who works at OK Tire, if need be Im sure they deal with this problem often and can fix it.