How do I safely wipe clean / clean install a Windows XP computer without its registration code OR the installation disc?

there is a high chance that there is a recovery partition on your hard disk that will restore the computer back to factory settings, different recovery programs are started in different ways, in my old xp computer you completely shut the computer down and then when you press the on button you repeatedly Press f10 button on the keyboard While The Computer Is Booting Up to be taken to the recovery program screen, in your computer you might have to press a different key when the computer is booting up

Some xp computers come with a recovery partition you can look under my computer to see if it has one if so google how to factory restore make and model.

If not you cant factory recover without a disk