Verify that halo2.exe is allowed through all firewalls and that all inbound and outbound connects are allowed for the executable. Also verify that the correct ports are forwarded. Default is UDP 2000 - 2008 and TCP 2009, however they can change based on which ever port is specified in the config file. (just add 9 to get the port range)
on google you can find many websites that will explain how to port forward through your router
