Account/Network Logon Changes

Recently, when I disconnect my notebook running WinXP SP1
from the network, I lose the ability to select domains in
the account logon screen (after pressing ctrl-alt-del). I
can only logon as administrator. After restring from a
previous restore point, it started working correctly and
let me logon to the network (my workgroup and domain had
changed). I turned the computer off last night, and this
morning, the same thing happened. Has anyone seen this
problem? Thanks in advance.