Windows 8.1 should transfer just fine, provided that the computer that previously ran it is no longer running 8.1. I had a laptop that i upgraded to windows 10 then I built my desktop. I was able to use that key to activate my windows, it took a little messing around to get it. If you call microsoft what they will tell you is to install your original operating system, so if that was windows 8.1 then thats what you need to install on your new computer. if it was 7 then 8.1 then that is how you have to install it. Once you activate it on that computer then you can go back and reinstall as windows 8.1 and move to 10 if you wanted. This worked for me.