Question : Network problem, cannot ping computers

I have 3 computers on a switch. That switch is connected to the rest of the network. There is a communications error somewhere with them. All 3 of them can ping the router and a server on the network. 2 of them can ping each other. Those 2 cannot ping the 3rd machine and the 3rd machine cannot ping either of the other 2. But they can all ping other computers. Oh, and the 2 computers can see the 3rd in Network Neighborhood, but they can't ping it.

Answer : Network problem, cannot ping computers

Have you checked the switch to see if there is any rules setup to avoid communications i.e. vlans? Have you checked the firewall settings on the computers that cannot communicate? Is there any anti-virus software that is blocking communication? Do you have a switch that you can swap out and plug the 3 computers into the switch to see if this solves the issue?