Changing the Windows XP product key may be necessary if you discover your current key is pirated or illegal but you don't want to reinstall Windows XP to activate your new legal key.
Changes to the registry are made in these steps. Take great care in making only the changes described below.
1. Click on Start and then Run.
2. In the text box in the Run window, type regedit and click OK. This will open the Registry Editor program.
3. Locate the HKEY_LOCAL_MACHINE folder under My Computer and click on the (+) sign next the folder name to expand the folder.
4. Continue to expand folders until you reach the HKEY_LOCAL_MACHINE\Software\Microsoft\WindowsNT\Current Version\WPAEvents registry key.
5. Click on the WPAEvents folder.
6. In the results that appear in the window on the right, locate OOBETimer.
7. Right-click on the OOBETimer entry and choose Modify from the resulting menu.
8. Change at least one digit in the Value data text box and click OK. This will deactivate Windows XP.
9. Click on Start and then Run.
10. In the text box in the Run window, type the following command and click OK.
11. When the Windows Product Activation window appears, choose Yes, I want to telephone a customer service representative to activate Windows and then click Next.
12. Click Change Product Key.
13. Type your new, valid Windows XP product key in the New key text boxes and then click Update.
14. If you're taken back to the previous screen and prompted, choose Remind me later.
15. Restart your PC.