brand new cap and rotor catastrophic failure!

while putting headers on my car I broke my old dizzy cap, so in replacing that I bought a new rotor as well. they are "BWD Select" I believe. drove GREAT for about 3 weeks, then I went out this morning and it just cranked and cranked. pulled plug wires to find no spark. pulled the cap to find a DESTROYED rotor and the cap has white chalky stuff all over it. what could've cause this? I have an ignition switch and starter button in the car, but I couldn't see why that would cause this.