How to uncover a long forgotten Windows product key
This information is encrypted so you will need help from
a free utility called Belarc Advisor, which you can download here.
Not only will this decrypt and show your Windows Product key, and those of any
other MS products you might have, it reveals a vast amount of information about
your computer's hardware and software, which it displays in a browser window.
By the way, be aware that you are only allowed to install a copy of Windows on
one computer at a time. Also, if you are using an OEM (Original Equipment
Manufacturer) version of Windows, supplied with a computer, it may not be
possible to install it on another machine, or you may run into difficulties
getting it activated.