Try typing one of the following in the chat line at the bottom, press enter after typing the command:
/server uk.quakenet.org
/server de.quakenet.org
/server se.quakenet.org
/server us.quakenet.org
This should try a different server to use for IRC. If you still can't connect, perhaps your LAN or ISP has prevented IRC usage (Some companies, schools, and ISPs don't like IRC).
What error do you get on connection?