Workstations can't ping server

I have a 5 computer network. The server is also a workstation. The server can ping all the workstations, but the workstations can not ping the server. The workstations can ping each other just not the server. But internet goes through the server to get to the workstations and they all are able to connect to the internet. Also there is a shared program that comes from the server and all the workstations can connect to it. But they can't ping the server. Thoughts?