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If you have had Windows 10 on the computer you should be able to reinstall Windows 10 without the need to first reinstall Windows 7. On a computer with Internet access, download the Microsoft Media Creation Tool from https://support.microsoft.com/en-us/windows/cre... . You should be able to boot from the USB key you create with that tool and reinstall Windows 10 without needing a product key because your computer will have a digital license on the Microsoft activation servers.