Check for following options on the client machines
1) Windows Firewall should be turned off or Open Port TCP ports 139 and 445 and UDP ports 137 and 138.
2) Simple File sharing should be disabled.
3) Verify that File and printer sharing for Microsoft Networks is enabled.
4) Admin $ and C$ shares are present
5 ) Check to make sure the computer browser service is set to automatic, if not set to automatic and start the service.