Are you sure your copy of Windows is genuine? Microsoft has this to say:
When you use Windows Vista, you receive the following error message:
“An unauthorized change was made to your license.”
To keep your system stable, you must go online and validate that your software is genuine:
This issue may be caused by hardware and software problems. Scenarios that may lead to this issue include but are not limited to following:
A hard disk error occurred.
A program that is incompatible with Windows Vista is installed. Examples of these applications include the following. (Other applications may also be incompatible with Windows Vista.)
Blumentals Software iNET Protector (all versions)
PC Tools Spyware Doctor (versions earlier than 4.0)
PC Tools Firewall Plus (versions earlier then 18.104.22.168)
Trend Micro PC-cillin Internet Security (versions earlier than 14.56)
Trend Micro OfficeScan (versions earlier than 8.0)
TuneUp Utilities (versions released earlier than 2007)
To troubleshoot this issue, follow these steps:
If you have one of the programs that is mentioned in the "Cause" section, restart the computer in safe mode, uninstall the software program, and then restart the computer in normal mode.
Note Contact the manufacturer of the software program for a version of the program that is Windows Vista-ready.
To uninstall a program, follow these steps:
Restart the computer.
Press F8 before Windows Vista starts.
Press ENTER to start Windows Vista in safe mode.
, and then type appwiz.cpl in the Start Search box.
Click appwiz.cpl in the Programs list.
Click the name of the program that you want to uninstall, and then click Uninstall.
Follow the directions on screen to uninstall the program.
Restart the computer in normal mode.
If the issue is not resolved, go to step 3.
Visit the following Microsoft Web site, and then click Validate Windows:
If the issue is not resolved, go to step 4.
Use System Restore to return Windows Vista to a point before the issue occurred. To do this, follow these steps:
Start Windows Vista in safe mode.
, click All Programs, click Accessories, click System Tools, and then click System Restore.
Follow the steps in the System Restore Wizard to return Windows Vista to a point before the issue occurred.
Perform a clean boot in Windows Vista. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
929135 How to troubleshoot a problem by performing a clean boot in Windows Vista
You may disable all the third-party programs. If the problem disappears, repetitively use the msconfig program to figure out which third-party program is causing the problem. Disable the program, or speak to the manufacturer about the problem.
For more information about Windows Genuine Advantage, visit the following Microsoft Web site: