Reverting to a restore point earlier might help but you likely dont have this option.
If you know of someone with XP Disc, you can use their Disc and use YOUR KEY that should be affixed to outside of computer. Just just need to identify which version of XP you have and then use media for that version.
I dont know of any tools to clean XP back to clean install state, none have been made probably because its just so easy to pop the disc in if you had one and wipe it and start fresh like an etch-a-sketch. Methods of setting it back to original build would involve lots of registry editing and then dealing with orphan files and installations. It would be a huge mess that is more of a problem then anyone I know would want to deal with.