Computer "SERVERNAME" cannot be connected. Verify that the network path is correct, the computer is available on the network, and that the appropriate Windows Firewall rules are enabled on the target computer.
To enable the appropriate Windows Firewall rules on the remote computer, open the Windows Firewall with Advanced Security snap-in and enable the following inbound rules.
COM+ Network Access (DCOM-In)
All rules in the Remote Event Log management group.
You can also enable these rules by using Group Policy settings for Windows Firewall and Advanced Security. For servers that are running the Server Core installation option, run the Netsh AdvFirewall command, or the Windows PowerShell NetSecurity module.
Because COM+ Network Access is not allowed you cannot use the Windows Firewall and Advanced Security MMC Snapin to remotely connect to the server. As a result you need to login to the Server 2012 core machine and run the following command from command prompt to enable remote access.
netsh advfirewall set currentprofile settings remotemanagement enable
Now you can remotely connect to the Server 2012 core machine using MMC snapins.
This article might also be of reference - Remote Disk Management of a Server 2012 core machine: