Have NT 4.0 PDC SP6a and 100 clients running Win98, NT 4.0 and W2K. Have Cisco switches between floors. They are fine. Having a sudden problem with various clients getting the No domain controller error (logging in with Cache). Also some of my servers are disappearing from Network Neighborhood suddenly. WINS and DHCP look fine. If I reboot my PDC all is well for a couple of hours. NIC looks fine and can be ping'd. Error 5719 Netlogon in Event Viewer. I have combed through the Knowledge base at Microsoft site and tried everything. I have event removed some of the Computers in Server manager, resynched, and readded to domain. Also tried having a client join a workstation reboot and then rejoin domain. This works for a little while then clients complain they cannot hit shares on a server and the server disappears from Netowork neighborhood. Any help would be appreciated.