If you receive an error indicating that your product key is not valid when installing Windows 7, it could be for the following reasons:
You might have mistyped your product key. Try retyping it.
You might be using a product key that doesn't match the version of Windows 7 that's installed on your computer. Check the product key to make sure it is for the version that you are trying to activate.
You can't use a product key for Windows 7 with Service Pack 1 (SP1) to activate a copy of Windows 7 without SP1.
The product key is for an upgrade version of Windows 7 and a previous version of Windows wasn't on your computer when Windows 7 was installed. To install an upgrade version of Windows 7, Windows Vista or Windows XP must be installed on your computer. If you formatted the drive before starting the installation process, you won't be able to use the upgrade product key to activate Windows 7. To activate Windows 7, you'll need to install your previous version of Windows, and then reinstall Windows 7. For help with the activation process, go to the Microsoft Support
For more information about Windows 7 activation errors, see Windows 7 activation error: 0xC004F061.
We recommend that you install Windows 7 with your current version of Windows running. If you want to format the hard drive, and you are using an upgrade version of Windows 7, you'll need to start your computer using the Windows 7 installation disc or a USB flash drive, click Custom (advanced), and then click Drive options (advanced).
To verify your product key, look for the product key sticker on your computer or inside the Windows package—or in a confirmation e‑mail if you purchased and downloaded Windows 7 online. Go to the Microsoft website to see examples of product key stickers.
If you still can't find your product key, you might need to buy a new one to activate Windows. You can purchase an additional copy of the same edition of Windows 7, which contains a product key that you can use. For more information, see Get a new Windows 7 product key.
If you're unable to enter a product key without getting an error message, you can leave the box empty and click Next, or you can click Skip. This will allow you to finish setup, but your copy of Windows 7 won't be activated. You must activate Windows within 30 days of installation. For information about activating Windows 7 after setup, see Activate Windows 7 on this computer and Activating Windows 7: frequently asked questions.
The product key won't be valid if you're running a non-genuine copy of Windows. For more information, see What is genuine Windows?
Article ID: MSW700002