The only reason you would not be able to connect to any IRC network is that mIRC is being blocked by either anti-virus or firewall software, or perhaps even by Windows itself. I have not come across any other reasons for this kind of issue (unless we also consider that you are using a network connection that is preventing such connections - but that's unlikely unless you are using mIRC from work or school). Also note that, as far as I know, you do not need to open up any router ports to connect to a server. If you find the solution, please let us know.