Although there are plenty of software applications that can change the product key installed in Windows XP automatically, but some users may prefer to manually change the product key by themselves. Changing or modifying Windows XP product key is not a common practice after installation, especially so if already activated, and that explains why Microsoft didn’t have built-in mechanism to edit the product key used in Windows XP.

However, for some reason such as the need to change the product key to newly purchased genuine product key, especially when the existing installation of OS is pirated or illegal. The situation also happens in big corporations which have volume licensing (VL) agreemnts with Microsoft, which tends to use a same VLK (Volume License Key) or leaked product key to activate all computers. To enter and make use of the new product key does not really require whole fresh re-installation of Windows XP. Follow the hacking guide below to remove and delete current product key used to activate existing copy of Windows XP, and force the OS to prompt user to enter new product key for activation.

  1. Click on Start and then Run.
  2. In the Open text box, type regedit and click OK to run Registry Editor program.
  3. In the left pane, locate and then click the following registry key:

    HKEY_LOCAL_MACHINE\Software\Microsoft\WindowsNT\Current Version\WPAEvents

  4. In the right pane, right-click OOBETimer, and then click Modify.
  5. Change at least one digit of this value in the Value Data to deactivate Windows.
  6. Click Start, and then click Run.
  7. In the Open box, type the following command, and then click OK:

    %systemroot%\system32\oobe\msoobe.exe /a

  8. When the Windows Product Activation window appears, click Yes, I want to telephone a customer service representative to activate Windows, and then click Next.
  9. Click Change Product key.
  10. Type the new product key in the New key boxes, and then click Update.

    If you are returned to the previous window, click Remind me later, and then restart the computer.

  11. For user using OEM system or volume license product key (VLK), repeat steps 6 and 7 to verify that Windows is activated. User should receive the following message:

    Windows is already activated. Click OK to exit.

    For retail Windows XP users, a 30 days registration for activation reminder will appear. User will have to connect to Internet for online registration and activation, or call the local Microsoft activation hotline for phone activation.