If you have the original media or the Certificate of Authenticity (COA) with a product key, visit the Compare Product Key Web site for resolution:
If you encounter a Windows Genuine Advantage (WGA) message that there is a problem with the product key or the volume license key for your installation of Microsoft Windows XP or Windows Vista, use one of the following methods to resolve the issue. Genuine Windows Microsoft Windows XP Home Edition Microsoft Windows XP Professional Microsoft Windows XP Tablet PC Edition Windows Vista Starter Windows Vista Home Basic Windows Vista Home Basic N Windows Vista Home Premium Windows Vista Business Windows Vista Enterprise Windows Vista Ultimate More.
