Lost server in workgroup

Had strange issue happen Friday afternoon. Have an NT4 SP6a server running an SQL application with three NT4SP6a workstations accessing an application from that server via the network. The application froze on all workstations and could no longer reconnect. Can not ping the server but can ping from the server the workstations. Workstations in the same Network workgroup can not access the server. Change to servers spare installed NIC and changed IP’s, change server netbios name and even created new workgroup and directly connect the server and a workstation with a crossover cable and still can?t ping or access from workstation to the server. Any ideas from anyone?