1. Navigate to the Microsoft Genuine Advantage--Diagnostic Tool webpage (see Resources).
2. Click the 'Start Diagnostics' button.

3. Click the 'Run' button if asked whether you want to save or execute the file. The program will return with the reason for the validation error.
4. Follow the onscreen instructions to correct the error. For example, if the diagnostic tool indicates that your product key is invalid, you likely mistyped a key or two--re-enter the key to correct the problem.
5. Reboot your computer once the process is complete.