I had a laptop with windows 7 home premium on it. When 8 came out I was able to get the upgrade for $15 since the laptop was relatively new. Now I am going to be building a new desktop and I am selling my laptop. I won't be able to use the 7 key obviously because i'm selling it so I am wondering if the version of 8 I have will work when I build my new desktop? or can it only be used on that laptop I had upgraded on?