What next? Mega2560r3 ATmega16U2 DFU Win8 USB

Using Arduino IDE 1.x
4

This page:

http://www.arduino.cc/en/Guide/Troubleshooting#upload

says:

The Arduino Uno and Mega 2560 use standard drivers (USB CDC) provided by the operating system to communicate with the ATmega8U2 on the board.