I am trying to activate Windows Home Single Language 10 (latest build 10586) using a Windows 8.1 Single Language Product Key.
But it's saying:
You are running Windows 10 Home Single Language. The Product key you entered cannot be used to activate this edition.
Error Code: 0xc004f210
I extracted the product key from the BIOS using the ProduKey utility when I was running Windows 8.1.
Here is a link to an article reporting that it's now possible to activate Windows with a previous Windows product key (from Windows 7 or later):
http://download.cnet.com/blog/download-blog/activate-windows-10-with-a-previous-windows-product-key/
I chatted with Microsoft Technical support; they said:
Ryan P
Basically "If you install this build of the Windows 10 Insider Preview on a PC and it doesn’t automatically activate, you can enter the product key from Windows 7, Windows 8 or Windows 8.1 used to activate the prior Windows version on the same device to activate Windows 10" meant the product key will not activate Windows because it is not a unique product key and is therefore blocked at the activation servers just like OEM keys are to prevent piracy. The free Windows 10 does not activate by key. It is an entitlement activation. Here is Microsoft's explanation.
I am not able to understand what exactly they meant.
As mentioned in comment/answers I tried clean install hoping it would automatically detect the key and proceed. Instead it requested a product key. And on manually entering the product key, it gives this error:
In case the image not clear it says:
The product key entered does not match any of the Windows images available for installation. Enter a different product key.
Best Answer
Pre Fall Update: You can't activate a fresh Win 10 install using a Win7/8 key. You'll have to install Win8 back to your computer and then update using Windows Update or run Setup from installation media while you're logged on Windows 8.
Post Fall Update: You can use a Win7/8 license key for a fresh Win10 install as long as the key was already used on the same machine before. Thanks to Tetsujin for pointing that out.