To find a lost Windows 7 product key, first look on the bottom of the computer to see if the information is on the manufacturer's sticker or check the installation disks that came with the computer. If the information isn't there, download a free key finder program, such as LicenseCrawler, that searches through the computer's registry, retrieves the information and then translates the product key into a usable format.
To use LicenseCrawler to find a Windows 7 product key, download the program, install it to the computer or to a USB drive, and then run it as an administrator on the computer for which you need the product key. This freeware program then searches the registry and retrieves not only the product key for the Windows 7 operating system, but also all the other registered programs installed on that particular computer.
Sometimes, newer computers have the product key built into their BIOS, allowing users to restore the computer to factory condition without the need to re-enter the product key. Should none of these options work, contact the PC manufacturer to see if it has a copy of the product key for that particular computer still on file along with other warranty information. If that doesn't work, users can contact Microsoft directly to get the Windows 7 product key for a cost of $10, as of November 2015.