***using my laptop that has windows 8.1 (acer aspire v3 551 8469)*** i didnt buy an optical drive with my rig but i bought windows 8.1 64bit oem version (the disk says windows 8.1 full version). so i went to go get the iso version of my product from microsoft and downloaded the windows 8.1 setup. i enter my product key (one that came on the packaging of the disk) and it says "this product key cannot be used to install a retal version of windows 8.1". so im stuck here not able to get a iso copy of windows to put on my 4gb usb for my new gaming rig?!?!