Bricked HDX 7 Thor ( Black Screen ) topic

Hello everyone, I was hacking my hdx hoping to put the CM11, but unfortunately in the build.prop change the inevitable happened.
now I can only go to stock recovery, the tablet starts, logo kindle fire gray and then black screen, I do not know how to go to fastboot, but I think I need a little ...
does anyone know how to fix this mess? :crying:
thanks in advance and sorry for my carelessness :)