Once you've paid for a Windows Product Key, then you don't need to pay for it again, but you should reinstall Windows or upgrade your motherboard which will certainly ask to enter the product code
If you can't see a sticker on your machine, then you can use free software to find the code. It is important to locate this code before you are asked to enter it.
Windows 10 is different from comparing to its predecessors Windows XP, Vista, 7, and 8.1, which aren't much use now. Using premium software such as Windows Recover Keys, or free like Magical Jelly Bean Keyfinder. There’s a good chance that this will give a generic number used by the manufacturers, and not one that will work to start your PC.
The steps are very easy in this route and it usually works well for Windows 7 and 8.1 systems without issue.
If you used the free upgrade that Microsoft offers during its early days or bought a digital copy from the Microsoft store, then you’ll have what’s called a Digital Licence. It means the Product Key is linked to your account, rather than kept as a sticker. So you can finish the process by logging into your Microsoft account whenever it asks “Enter Your Product Key”. Remember that you need internet access for this to work.
If you have Windows 10 PC then you can check whether you have a Digital License or not by navigating to Settings>Update & Security>Activation and check whether it shows that ‘Windows is activated with a digital licence linked to your Microsoft account’.
This means that as long as you use your Microsoft account to login to your device, you don’t need product key to activate Windows 10.
If you haven't linked to your account, then follow these steps;
Open the Settings
Click 'Sign in with a Microsoft account instead' and Sign in
Create a PIN code or click the 'Skip this step' option
The alternative way to find your Product Key is to look for the 25-character code that came with or on the packaging that accompanied your device. This will either be a card inside the box, a sticker, or printed upon the Certificate attached to the PC.
According to HP, they do not imprint product key on laptops or PCs for security reasons. As with Digital Licence, the product key will be stored somewhere in the computer and it will automatically get activated if needed.
Since Microsoft has your ‘digital signature’ and it recognises the combination of components when you install and automatically activates the Windows. This means you can skip it when Windows update asks for a product key during the installation process.
It’s just annoying that there’s no message to tell you this: the screen is mainly for those installing the latest version of Windows 10 update which they’ve purchased and therefore it still requires a product key.
So, even if you skip that screen on the installation step, Windows 10 should activate as long as you haven’t made any big changes. Upgrading a HDD hard disk to an SSD won’t affect anything, nor changing your graphics card. But upgrading your motherboard or processor will mostly count as ‘significant change’ and you’ll have to call Microsoft support if you find that Windows is no longer activated.
A product key is needed when uninstalling or reinstalling Windows. Generally, if you bought a physical copy of Windows, the product key should be on a label or card inside the Windows box. If Windows preinstalled on your PC, then the product key should be on a sticker on your device.
If your product key is scratched, blurred, immediately contact the retailer who sold you. If your retailer isn't able to help you, then immediately call our Microsoft help.