you should give more info like root status, kernel status, rom status etc.
try this
make sure your phone is disconnected while following all these steps-
0)try with usb debugging enabled.
stop here and try now, if it is resolved otherwise continue.
1)uninstall kies and samsung drivers strictly via programs and features.
2)reboot.
stop here and try now, if it is resolved otherwise continue.
3)install latest samsung drivers - 5.0.16.0 i think (don't install kies bs in any circumstances)
4)reboot.