windows xp pro login

I have XP Pro on a laptop and have the domain login screen come up when Ctrl-Alt-Del is pressed.
When you type in your user ID and password for NT 4.0 or 2000 and you have the domain ID and not the computer selected, and your laptop is not connected to the domain they give an error stating the domain is not present. I have been able to type in my user ID and password and domain in the logon and get into the laptop. I go to the users icon in control panel and my user ID is not there. Does anyone know how this can happen? and how do I fix it so that if you are not phisically attached to the network you can’t log in