On the Certificate of authority label on the computer, or in the package when you buy a legitimate copy.

Each key is unique and can only be linked to a single PC. using the same or a random key just gets the computer(s) using it flagged as having a fake copy of Windows...

When you buy W 8.1 Pro legally, you also get a legal Activation Code.

Sooooo:

What are you NOT telling us???

Would buy from them again windows anytime upgrade from starter to home basic key

You should buy a genuine copy of windows.

Its illegal to download a copy and crack.

Though, if u do u shouldn't publish this type of topic in public

Thank