SBS2000 freezes during logon screen

We have a SBS2000 running in our office. We are having a
problem with the logon screen saver. If we start up the
server but don't logon, after awhile the screen saver
comes on and we can't get back to the logon screen cause
the computer froze. The only way to get back to the logon
is to physically turn the computer off. Does anyone know
how to stop this from happening?

Thanks in advance,
Jenn