2000 member server in NT4 Network

I am installing windows 2000 server on a PIII 766 256 mb ram, the problem is the system works fine for 5 to 10 minutes on the network i can access any n/w resource during this time, but after that the tcpip & NETBEUI gets disabled, and i am unable to access the network also i am unable to ping the server or any host on the n/w, i formatted the system and reinsatlled freshly, changed n/w cards, installed from another cd, changed n/w points, installed 2000server on other machine but the same problem is persisting.
i am installing the 2000 server as MEMBER SERVER, also i tried to install in WORKGROUP mode also but the problem is same. the setup is NT4 server as Pdc and 98 clients. all the systems are working fine only this system with 2000 os is giving problem.