Where did my PDC go?

Windows terminal Server 4.0 and Citrix metaframe 1.8.
In network neighborhood I can not see the PDC for the network.
This is causing no apparent problems.
I reboot the PDC and it appears, then it disappears.
I can \\pdc\c$ at the run command,I can browse the network,
I can login on terminals, fat clients.
What's going on?

Thanks for any input.
Dave