Arduino uno cannot be seen in devices on windows 8

Hi

My original problem was the serial port option being greyed out on my windows 8.1 computer. After some research I found that you need to update the drivers manually from device manager. My problem here is that device manager will not recognize the uno or even show 'other devices' for that matter.

The arduino lights up as normal and have had no problem with it on my old mac in the past.
Does anybody know how to get the arduino read and then fix the driver/ com port problem on windows 8.1?

Thanks