Log-in password glitch

I have an XP Pro machine joined to a Win 2000 server domain. Recently I had changed it to join a workgroup instead in order to use it to access files on a computer in a remote location that is not joined to the domain. When I rebooted the computer it came up requesting my user name and password. It had displayed my last user name that I logged in with but when I entered my password it would not accept it. Neither would it accept Administrator and the password. When I attempted to boot it from the command prompt it still would not accept the password. Help………..