How to Authenticate Windows

1. Activate you copy of Windows. If this fails, you may have an invalid copy.
2. Browse to Windows Update. By default, Windows will put a Windows Update link at the top of the Start menu in all versions except Vista. With Vista, the link is within the Control Panel.
3. Go through the initial questions until you get to the step 'Authenticate Windows.' Push the button to start the process and wait a few moments. Your version of Windows is sending information about itself to the Windows Update system. If your copy is valid then you may continue to update. If not, Windows Update will halt and inform you that you may have a fraudulent copy.
4. Contact Microsoft using the information provided by Windows Update. The representative will help you figure out if it was an installation error or if there's actually a problem. If you're certain that your copy is legitimate and it fails the authentication, the representative should be able to get you running in just a few minutes.