I usually don't link to non-microsoft pages, but I couldn't find a 'How
To' with screen shots. The below URL shows how to get to the Change
Product Key section, within Windows 7.
http://www.sizzledcore.com/2009/10/26/how-to-change-windows-7-product-key/
You can also try the Command Line to change the Product key:
Click on the Start Button and type: CMD (into the 'Search programs and files' field in the Start Menu)
The Start Menu will show 'CMD.exe',
Right-click the CMD.exe file and select Run As Administrator.
In the CMD window, type: slmgr.vbs -ipk <type your product key here>
To activate windows after changing the key, type: slmgr.vbs -atoHope that helps...