Cannot log onto domain

[S.Low]

My laptop cannot log on to my office domain suddenly. It
has been working fine for about a month. The error
messages either say I do not have permission, I do I am
the administrator on both systems, or that it cannot
connect to the server. The messages tell me it is
talking to the server, but some how has lost permission
to access it. Is there some setting in XP that kills a
network logon after a certain time?
Any assistance welcome personal or web based

Thank you
S.Low