I want to make a USB backup of 8.1 where I can either install it from my legal Windows 8 Pro upgrade or from the 8.1 usb stick itself (even if I have to install it twice like we did with windows 7). I managed to make a 8.1 pro USB stick (made from neighbors iso file) where he has the full version I have the upgrade same windows essentially. However when I went to test it .. it says my key isn't valid. I just don't want to have to download 8.1 anytime I might have to redo my system (I know I can make a backup with paragon and other programs but I think everyone gets the point as what Im looking for here). Can a 8.1 usb stick be made using my legal Win8 Pro Upgrade key?