For an installed copy.
Download the free utility SIW - System Information for Windows,
From the menu click on Licenses, all installed keys will be revealed.
SIW is a standalone utility that does not require installation (Portable Freeware) - one less installed program on your PC as well as the fact that you can run the program directly from an USB flash drive, from a floppy, from a network drive or from a domain login script.
http://www.gtopala.com/