I've got the same exact issue, but with the Uno. There is no indication whatsoever that the board is interacting with the computer; it's not showing up in Device Manager anywhere or telling me that there's an unknown device. I'm on Windows 7, and I'm also having issues getting it to talk to the Mac. When I plug the board into any USB port on any of my machines, the green light shows that the board has power and it runs the default Blink sketch but I have no way of uploading sketches or updating the driver from the computer. I've tried hitting restart on the board, plugging it into all different ports, and tried multiple USB cables. I've scoured the internet for solutions to this problem but many solutions seem to occur through the Device Manager, but that doesn't seem to be possible in my case.
Could it be a problem with the board?