issue with client

I was setting up a second computer for testing purposes but for some reason the client cant connect to server however my other computers can just wondering if there are any known issues as to why this would not function this one is in my own house however i have been able to get another computer working outside of my home so i know the server is functioning correctly i just get an error that i cannot connect to server i have disabled firewalls reinstalled game completely not sure what may have gone wrong any help greatly appreciated thanks