Pre-installed OEM version of Windows

If you purchased your PC with Windows already installed from a large manufacturer such as Dell, HP or Toshiba, it's likely that Windows was installed using an OEM key instead of the actual key for your PC. This saves them (and you) money because it's much more efficient for these large companies to install Windows once and then clone the drive.

That's why key recovered may be incorrect. Please note, that if your Windows product key differs from product key on your sticker, the correct key is on sticker