Activate Windows 10 using a product key

A product key is a 25-character code, that looks like this:

PRODUCT KEY: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX

• During installation, you'll be prompted to enter a product key. Or, after installation, to enter the product key, select the Start button, and then select Settings > Update & Security > Activation > Update product key > Change product key.

• You’ll need to use a valid product key to activate Windows 10 on a device that has never had an activated copy of Windows 10 on it.
  
  
• You’ll also need to use a valid product key if you're installing an edition of Windows 10 that wasn’t previously activated on the device. For example, you'll need a valid product key to install and activate Windows 10 Pro on a device that had Windows 10 Home installed.
  
  
• During the installation, you’ll be asked to enter a valid product key. After the installation is complete, Windows 10 will automatically be activated online. To check activation status in Windows 10, select the Start button, and then select Settings > Update & Security > Activation.

• During reinstallation, you’ll be asked to enter a product key. When you type in your product key, you will have an activated edition of Windows 10.
  
  
• If you finished setup and did not enter your product key, you can still enter your product key. Select the Start button, and then select Activation > Update product key > Change product key.

• When you make a significant hardware change to your device, such as replacing the motherboard, Windows 10 might no longer be activated.
  
  
• If you do not reinstall Windows, then you can select the Start button, and then select Activation > Update product key > Change product key to reactivate your device. Otherwise, you can enter your product key during the installation of Windows.