The built in admin hides by design. No problem, create a new backup Admin account. As this is so well discussed such as google "How to unhide the XP admin account" I'll stop here.
But repeat. Do not use Windows without spare admin accounts.
Rookie question so I put it in "Rookie" forum. I have "ancient Dell Optiplex PC w/ XP Pro. I created a "Second User" with separate log-in password. Now my original ("ADMIN") log-in page has disappeared. When I do the START>LOG-OFF>SWITCH, all I get is the new second user log-in (no ADMIN). What happened to "ADMIN" log-in and how do I get it back?