If you are unable to connect to any servers on an IRC network, it may be that the IRC network is experiencing problems in which case you would need to contact the administrators of that IRC network to ask for help.
The Undernet IRC network has a website
and a forum on that website where you can ask questions. Perhaps someone there may have a better idea.
The only Undernet server I am able to connect to is the one in Los Angeles, using the command /server LosAngeles.CA.US.Undernet.Org but that may or may not work for you.