1)There are 4 system configured in LAN network with Workgroup domain. I could able to give a print from a system. I can ping all the system. Even disabled the Firewall too.

2) In RUN->\\ ip address is given. I get the error stating The network connection cannot be reached. I cannot even share the system too. Can u help.

I suspect the router or switch.

If one or more nodes is not functioning you should check your configuration on app four computers then check the networking equipment test the cables and if it is only one node down you should try another port on the switch if one is available.