Fix Windows XP Activation infinite loop

Under certain circumstances Windows XP can get stuck in an loop where it continually asks you to active the product, but the activation wizard tells you that it is already activated.

To fix this download the Windows Product Key Update Tool and then run through the steps below to change the key. Reboot the PC when asked, and you should now be able to boot into Windows.

Be careful though, because I have seen the Windows Product Key Update Tool crash making it impossible to boot into Windows, so always backup first.

You may need a second XP key as the Product Key Change Tool usually won't allow you to update the key with the same key, but you can always use the tool twice to change it back.

You may also be able to use the fix from Microsoft here.