I found this thing when I wanted to change my Win XP key to another key. There is a key changer that you may download from the Microsoft's website, but it's useless. So, i googled around and found this trick. It worked!
How To Change Windows Xp Sp3 Product Key Product
To use the most appropriate Windows XP product key the following steps are recommended. Open the properties option after right-clicking on Start and then Computer. Click the activation windows option. By accessing this option, the user gets the chance to alter the Windows XP Professional product key. 'A small application that allows users to easily change Windows XP product key number by entering new valid XP product key into the field provided and the just press the ‘Change Key’ button. Then the application will run the patched activation process so that the Windows is fully activated after reboot.'
How To Change Windows Xp Sp3 Product Key Office 2016
It is very useful nowadays because the student key v2c47-MK7JD.........is not genuine anymore. So in order to change it, you might be needing this method otherwise you have to reformat your computer and install it with a new key. This method worked like a charm. It's not that difficult though....Here it is
Click on Start and then Run.
In the text box in the Run window, type regedit and click OK. This will open the Registry Editor program.
Locate the HKEY_LOCAL_MACHINE folder under My Computer and click on the (+) sign next the folder name to expand the folder.
Continue to expand folders until you reach the HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsNTCurrent VersionWPAEvents registry key.
Click on the WPAEvents folder.
In the results that appear in the window on the right, locate OOBETimer.
Double click on the OOBETimer.
Change at least one digit in the Value data text box and click OK. This will deactivate Windows XP (yeah just type anything and OK)
Click on Start and then Run.
In the text box in the Run window, type the following command and click OK.
%systemroot%system32oobemsoobe.exe /a
When the Windows Product Activation window appears, choose Yes, I want to telephone a customer service representative to activate Windows and then click Next.
Click Change Product Key.
Type your new, valid Windows XP product key in the New key text boxes and then click Update.
If you're taken back to the previous screen and prompted, choose Remind me later.
Restart your PC.
Good luck!