I'm thinking of upgrading my laptop that came with Windows 8 x64 O.E.M. and has been upgraded to 8.1 x64 to 8.1 Pro x64 over the weekend.Can I do a clean install of 8.1 Pro with the product key that Microsoft give's me with the 8.1 Pro upgrade. I already have 8.1 Pro on a usb flash drive that...