XP Login

Before I go searching endless answers…….
My login has got to be corrupted. It does not show up on the welcome screen (my login box). Logged in (it boots automaticlly into it using TweakUI), I go into USER ACCOUNTS and my account is set on LIMITED. It was originally ADMIN. I can not change it back because it is not in the WELCOME SCREEN.
Any dieas how to fix this, or is creating a new login the way to go?