If your Windows product key isn't valid, if you don't have a Windows product key, or if you've lost the product key that came with Windows, you'll need to buy a new one to activate Windows. To learn how to find your product key, see Where do I find my Windows 7 product key? For more information, see Windows 7 activation error: invalid product key.
You have 30 days after installing Windows to activate it online or by telephone. If this 30-day period expires before you complete activation, some Windows features will stop working until you activate your copy of Windows. For more information, see Activating Windows 7: frequently asked questions.
To obtain a new genuine Windows 7 product key, you'll need to buy an additional copy of the same edition of Windows 7, which contains a product key that you can use. For more information about how to get Windows 7 in your country or region, go to the Shop webpage. You can also purchase Windows 7 at retail locations.
If your Windows product key is not valid, if you don't have a Windows product key, or if you lost the product key that came with your copy of Windows, you'll need to buy a new one to activate Windows. You must activate Windows online or by phone within 30 days after installation to use every feature of Windows.
To get a product key, go to the Microsoft website.