dali

I have been having a periodic network communication problem between 2 workstations and the server. When communications are interrupted neither WS can address the server. Visually the NIC displays look normal 1 solid and 1 flashing. Also, there are other pc's connected via the router that are not interrupted as well as pc's that are able to communicate via the network with the exception of the server. The problem is usually resolved after turning off all the associated equipment and rebooting all pc's. Sometimes it doesn't work the first time and takes several iterations. Once it starts working it continues. I did replace a switch once and it worked after that but I think it was a coincident not the problem. I have wondered about replacing cabling, NIC's and the router. Any suggestions will be appreciated. Thanks. Dick.