Can I use a Windows 8 key that I bought on a new PC?

I had a PC recently. It had Windows 7 on it and I eventually bought a Windows 8 upgrade key. Then the computer died and I switched to Mac. I have an old different PC running Windows XP. Since the original computer is dead, is it possible to use the same key again? When I tried just now it said I can't use an upgrade key to install windows 8, which doesn't make any sense to me.

you need to download and create the "Newer" windows 8.1 setup media (link in sig below) you need a win7 or better pc to download the media..

Windows 8.1 was never intended to install (without a few hardware issues) on a XP machine

This is not a windows 8.1 key, its a windows 8 key

How to transfer Windows 8/8.1 license to new computer. -> link

Note: This Windows 8.1 installation media accepts Windows 8/8.1 product keys, both OEM and retail (for example, "Windows 8 Pro $15/$40 Upgrade Offer" product key).

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The activation page shows the following message (see screenshot below):

This product key is being used on another PC. Please try a different key.

Note: Click on the Call support option (see screenshot below).

Note: The activation robot asks you how many PC's you have installed Windows on. The correct answer is number 1.

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