If you have a legitimate license (e.g., from an old sticker or purchase), you can use that key for reinstallation. Otherwise, for a legal and secure system, consider upgrading to Windows 10/11 (where a free upgrade path from genuine 7/8.1 may still work unofficially) or using Linux.
These official keys from Microsoft are designed to configure Key Management Service (KMS) clients. They bypass initial configuration prompts but require connection to an active license host server to achieve fully authenticated permanent status. (Windows 7 Professional N) W82YF-2Q76Y-63HXB-FGJG9-GF7QX (Windows 7 Professional E) Shared Retail & OEM Public Keys windows 7 professional product key free