The firmware update sometimes fails for various reasons and the Mionix Naos 8200 will not respond. This can be resolved by running the firmware update after the mouse is set in to bootloader mode.
To set the Mionix Naos 8200 in to bootloader mode hold down the right mouse button and the scroll wheel button at the same time while you plug the mouse in to your USB port. Then run the firmware update that is located in your Mionix Naos 8200 folder on your computer.
If you still encounter problems, try run the firmware upgrade from another computer.