A Windows product key is a 25-character code used to activate Windows. It looks like this:
PRODUCT KEY: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX
Locate your product key for Windows 10
Depending on how you got your copy of Windows 10, you'll need either a 25-character product key or a digital license to activate it. A digital license (called a digital entitlement in Windows 10, Version 1511) is a method of activation in Windows 10 that doesn't require you to enter a product key. Without one of these, you won't be able to activate your device.
Where to find your product key depends on how you got your copy of Windows.
Select any of the following to see more information:
If your product key is scratched, blurred, or otherwise unusable, contact the retailer who sold you the product. If you aren't able to get help from your retailer or have already tried and couldn't get a working key, call Microsoft Support.
For more information about digital licenses and product keys in Windows 10, see the “Methods of Activation” section in Activate Windows 10.
Locate your product key for Windows 7 or Windows 8.1
A product key is usually required when uninstalling or reinstalling Windows 7 or Windows 8.1. Generally, if you bought a physical copy of Windows, the product key should be on a label or card inside the box that Windows came in. If Windows came preinstalled on your PC, the product key should appear on a sticker on your device. If you’ve lost or can’t find the product key, contact the manufacturer.