Hi Gummy.Worm,
I am Dave, I will help you with this.
Removing the key does not deactivate Windows immediately, that will happen with a future update, there is no real deactivation method in Windows any more because of digital licencing.
What happens when you install the key on another PC, that then indicates to the activation service online to deactivate the old PC.
Have you tried using your product key on the new PC?