If you are trying to activate Windows 8.1 on a computer that originally came with it, you likely do not need to buy a new key.
: When you reinstall Windows 8.1, the installer should automatically detect this key and activate the system without prompting you to enter one.
: If it doesn't activate automatically, you can use a tool like NirSoft ProductCDKeyViewer to retrieve the embedded key from your hardware. 2. Reputable Online Marketplaces
Purchasing a product key in 2026 is no longer possible through official Microsoft channels , as Microsoft discontinued sales and official support for the operating system on January 10, 2023 .
If you need a new license for a different machine, your best options are established third-party software resellers. Where to buy a windows 8.1 product key - Microsoft Learn