Nt 4.0 server network

I set up a development network, PDC, BDC, member server. When the PDC first boot up, The Bdc and the member server can browse the network and see the PDC, But after one hour,
The PDC drop off from the network neiborhood from the BDC and the member server.
I set up the host file/Dns/wins. But the problem still exist. Please help.

Thanks in advance.
Tbui@medcellbio.com