If you have a dead installation of Windows XP that cannot boot anymore, you may want to format the disk and reinstall your Windows XP with the same CD Key that you used in the original installation.

But what can you do if you lost the original CD Key ?
If the Registry files of the unbootable XP are still intact, you can use the ProduKey utility to retrieve the original product key that you used for installing this XP.

In order to do that, follow the instructions below:

1. Attach the disk of the dead Windows XP to another computer with Windows operating system that works properly.
2. Download ProduKey.
3. Run produkey.exe
4. In the 'Select Source' window, choose 'Load the product keys from external Windows directory'. (If you didn't get the 'Select Source' window, press F9).
5. Type or choose the Windows directory of the unbootable Windows XP. It should be something like E:\Windows.
   

6. Click the 'Ok' button. You should now see the desired product key in the main window of ProduKey.