The other question is, what kind of computer is it? If it’s one of the major brands, it may have a hidden reinstallation partition on the drive that will allow for restoration of the original OS. On Dells, I think it’s accessed with F11 at boot time.
Also, if you Torrent the correct Windows 7 reinstall disk for a major brand, you often won’t need a product key to reinstall as the key (or a generic brand-specific key) is saved in the system’s firmware.