On Windows 2012r2 server core, the firewall is enabled with the public profile on installation, so just enabling RDP in sconfig does not allow RDP access.

You can enable RDP to pass through the firewall with the following powershell command

netsh advfirewall firewall set rule group="remote desktop" new enable=yes

Alternatively, you can enable RDP and configure the firewall with the following

cscript C:\Windows\System32\SCRegEdit.wsf /AR 0