all new brakes , why then ?

I just replaced the rotors wheel bearings pads ,everything looks great.
backed outa the drive no problens drive forward all is good, hit the brakes.............. grind like steel on steel !
i just dont know wth. is up ) , jacked up off the ground the wheels spin fine no drag on them nothing looks good .
i only get the sound going forward when i hit the brakes. after driving 1/4 mil , slowly there is no visable damage to the rotors inside or out .
any ideas ?
 clueless here ~
thx ...