Hi, this is really a different type of post, could be considered as radical too. Because almost everywhere in the Internet you see the posts describing how to activate the Windows (either genuinely or using any cracked piece of software or some fake serial key). But this post in contrast describes how to deactivate the Windows.
First why do you want to deactivate the Windows ? Simple, you may want to deactivate the Windows for several reasons, but one main reason is to install another serial key with a different edition. You can always do this without deactivating the current one, but still in few circumstances you may need to deactivate the Windows.
Deactivating the Windows is quite simple, just a simple command line statement. Open CMD in the Admin mode. Then type the following slmgr.vbs –upk and enter.
This will remove the current serial key from the Windows and leaves the OS in the deactivated state.
Versatile Digital DNA 
And can the key be used in another machine, once the key is deactivated from the current machine ?
The answer is Yes & No. 🙂 It’s based on your license type. If you’ve a multiple machine activation key, Yes of course you can do this even without deactivating the key. If you have purchased the OS for yourself with single user license you can deactivate and use it on another machine. In case if you’ve got the OS through an OEM license it’s bit complicated and subjected to OEM rules and regulations of the specific vendor.