xt912 fastboot flash help topic

hello to everybody sorry if i duplicate any posts but here is my problem i have a xt912r from verizon and i accidently broken the original jb firmware and now i have a phone that doesn't work anymore i tried to put it in fastboot mode but is not recognized in any way in windows xp/7 or linux distributions the only way it's recognized is the sb flash mode but rsd lite gave me an error the phone couldn't go in fastboot so i cannot flash it in fastboot what can i do i have a factory cable but it gave the same error i tell above "the device couldn't be recognized and it has been stopped" <--(this in windows ) and ubuntu etc it wont appear even in the terminal with the command lsusb what can i do please help me im breaking my head on it thanks to all and sorry for my bad english