After you install a Windows Vista service pack, you may be prompted to activate your copy of Windows Vista. You may be prompted to do this even if the computer was previously designated as "Genuine and Activated." Additionally, the Vista System Properties dialog box may indicate that your copy of Windows Vista is not activated.
Cause 1: Changes to hardware or to hardware device drivers are detected
Part of the Windows Genuine process requires you to reactivate your computer when certain hardware is changed or when certain hardware device drivers are changed. Windows Vista service packs may update some installed device drivers. Therefore, you may be prompted to activate Windows Vista again.
Cause 2: The copy of Windows Vista that is installed on your computer was not activated
Before you installed the service pack, an activation exploit may have been installed on your computer. This activation exploit may have been created to circumvent the Windows Vista activation process. This kind of exploit can cause extreme alterations to important system components in Windows Vista and can affect system stability. Service packs address exploits that are created to circumvent the activation process. These service packs also include updates that target and disable these exploits.
Note For more information about how to determine whether a copy of Windows Vista is genuine, visit the following Microsoft Web site:
After you install a service pack on a Vista-based computer that is running this kind of exploit, the Vista activation process is reactivated. You may be prompted to activate Vista and to provide a current and valid Windows Vista license key.