Purchased an HP Pavilion 500 that came installed with Windows 8. When it became available, upgraded the OS to Windows 8.1 without issue.
I used a Product Key finder software app to retrieve the Product Key for this machine.
Recently, when I went into Windows Update and selected the 'Add features to Windows 8.1', I entered the Product Key at the prompt (without entering the dashes), and I got the message: "This key won't work. Check it and try again, or try a different key."
Is the OEM product key restricted?