Yes. Microsoft’s free upgrade offer technically ended, but the servers still accept valid Windows 7/8.1 keys to activate Windows 10. Clean install using the ISO and enter your old key.
Check the file size – a genuine 64-bit Windows 10 ISO is between 5.2GB and 6.0GB. Also, verify the SHA-1 hash against Microsoft’s official values (available via PowerShell’s Get-FileHash ).