When you installed the drivers did you run it as administrator? If not uninstall the drivers through control panel (uninstall appications) reboot your computer, then right click the driver installer and choose run as administrator. Once that installs I would reboot both computer and phone for good measure.
BSand, I have a few ideas! Let's make sure your phone is recognized by your computer. Try re-installing your Samsung drivers from Samsung's website: http://bit.ly/TVV8Y7. Then try Tidbits suggestion if still having issues.
Let me know if you need further assistance.
Follow us on Twitter @VZWSupport