Windows 10 downloaded, without product key

[legocreation27]

I downloaded Windows 10 on my new built PC using a flash drive. However, I do not have a product key. Where can i find just the license/ product key without installing windows again as I have never done that before with ANOTHER flash drive?

 

[Dark Lord of Tech]

Go to Microsoft and buy a key , then enter it in the activation window.
https://support.microsoft.com/en-us/help/12440/windows-10-activation

 

[Calvin7]

With any details of how you created Windows 10 installation media lacking, I doubt anyone would know where it came from or why you don't have a license/ product key.