Vista product key is not validating
Certain versions of Windows and Office are available under a volume license, where a single product key is used for multiple installations.Programs purchased under this license must still be activated, with the exception of Windows XP and all versions of Office released prior to Office 2010.
On each boot, Windows confirms the presence of specific information stored in the BIOS by the manufacturer, ensuring the activation only remains valid on that computer, even if the product key is used on another machine.
Changing the product key that you used to install Windows with might be necessary if you find out that your current product key is...
well, illegal, and you've purchased a new copy of Windows to solve the problem.
Thus in some circumstances, where you unable to activate or fail WGA validation due to compromised, leaked, blocked or violated product key, you can change Windows Vista product key after installation, without the need to reinstall Windows Vista.
To change Windows Vista product key, use the following steps: If Windows Vista system already in Reduced Functionality Mode, there is an option of “Retype your product key”, which is the same as “Change product key” above and will give you the opportunity to enter a new product key or license key if you want to activate Windows Vista with a new key that is not yet installed on the existing installation of Windows Vista.