Go to settings, press "more.." select USB Connection, press button, then plug in phone to pc.
Also go http://www.samsung.com/us/kies/ for Kies that bypasses all that. If that doesn't work then replace your cable with a "data cable". You also might be using a charging cable which doesn't have data support connecters in it.
This one will work:
http://www.ebay.com/itm/MICRO-USB-data-line-general-cable-for-HTC-Mobile-phones-adapters-TOUCH-HD2-T8585-/171018490106?pt=PDA_Accessories&hash=item27d17f10fa
I know it says for HTC, but its for all micro usb ports.