Actiate Win 8.1 pro with Win 8 product key

Hi..
I have Dell Inspiron 1531 laptop with Win 8 Preinstalled.I installed Win 8.1 pro with USB.
Now I want to activate 8.1 with product key of win 8 which I found from BIOS through a tool after installing 8.1.
But it is showing the "The key doesn't support this version" like that. I want to activate Windows 8 or 8.1.I don't have any installation CD of windows 8.

Hi

Have you bought Windows 8.1 Pro key from Microsoft? If so, you can download the Windows 8.1 Pro ISO by following Option 1 in this tutorial and make a UEFI bootable USB. Do a clean install , enter the Pro key for activation.

Download & Create Windows 8.1 installation media

If not, check which version of Windows 8 was pre installed in your laptop (Core, Single Language Core etc.) & download the appropriate ISO by following the above tutorial and make UEFI bootable USB. Then do clean install. The Windows 8 OEM BIOS key will automatically activate the Windows 8.1 install if they're same edition.

If the original OEM install was just 8.0 (Core) and not 8.0 Pro, that key will not work on 8.1 Pro. You need a Pro Key. If this is true, you should have installed 8.1 (Core) not 8.1 Pro. You can get 8.1 (Core) via the link Visruth posted.