Mirc defaults to a Random Dalnet server
If your just trying to make a connection and Dalnet is trying to be used you will not connect to a server.
Dalnet has gone thru a number of changes with servers dropping them, DOS Attacks, servers refusing connections, etc. You will find a large number of posts here explaining that.
If you want dalnet goto this web page
http://edk.dyndns.org/servers/It will show the servers on dalnet that are accepting connections.
Otherwise try a different network like Phazenet, Undernet, Efnet, etc.