Due won't show up in port but Duemilianove works. Solved: changed the usb cable

I can't upload to my Arduino Due board, it is not being found and ports is greyed out. I installed the package so I can select the board type under 'tools', and tested both ports. I'm not sure what the issue is, as my arduino duemilianove works fine.

Sounds lkke you were using a damaged, defective, or charging only usb cable. Charging only microusb cables are very common (as well as cables rigged with voltage dividers to the data lines to tell old phones they can charge faster than 500mA from a dumb charger)