You can download Windows 10 or 11 from Microsoft and use it without a key. It will be safer than Windows 7, though some customization features will be locked.

One of the most reliable ways to get a legal license is by purchasing a refurbished machine that already includes a COA (Certificate of Authenticity) sticker with a valid product key. Critical Risks and Considerations

Many "cheap" keys sold online are "high-quality counterfeits" or MSDN keys that may deactivate after a few months, often after buyer protection windows have expired.

You may still be able to use a genuine Windows 7 key to activate a newer, supported version of Windows.

Since official sales have ended, you must rely on third-party resellers. Current market prices typically range from .