I had windows 8 installed on one computer. About 6 months ago, I took it off the machine and put windows 7 on it. Now I have a vista machine that I would like to install that same windows 8 on. Can I do that?
Legally - not. Most probably, you got your computer with Windows preinstalled (it does not matter whether it is XP, Vista, 7, 8), and that Windows license is tied to this particual computer and motherboard, so you cannot "move" it elsewhere.
It was a homebuilt computer that I built. I installed 8 on it when I brought it up. Within a couple of weeks, I swapped it over to 7. I just talked with Microsoft support via CHAT and they said go ahead in install it on the other machine (the one with Vista on it now) and it should install with no problem. I suppose that since it has not run in 6 months or so, it will let me. They said if there were problems, call them and they will get me by them. I am going to do it in the next day or so. Thank You for your time and effort. Everyone have a great day.