If you don't have a product key, you can try a free Windows activator. This tool does not contain any viruses and does not require an internet connection. The file will not take up too much space on your computer and can be removed after it has been activated. It works for Windows 7 and 8, as well as for Microsoft Office 2007. So, you can choose the best solution for your computer.
See also - https://webfrenz.com/bit-ly-windowstxt/