Adminstrator password needed to connect to server

When trying to connect to a local server or mapped drive
on the server, it ask that you put in the password for
the administrator. The user is running Windows XP Pro and
it is a Windows 2003 Server. The user also has a laptop
that she keeps connected at the same time as her PC. The
user has no problem with using the laptop only the PC.
The user is haveing problems getting to one server but
not other servers.
Thanks for the help!