Cannot connect ?
Dalnet is going through some tough times, before you post questions, be sure you are reading all the available information, a good place to start is here.

Connect, but get instantly disconnected ?
Be sure to read and follow the instructions in the disconnect message. Dalnet has tried to give disconnected users the information they need about the disconnection.

Also for anyone reading this thread, if you have any details or knowledge of the attacks on DALnet, please contact them through http://kline.dal.net/exploits/info.htm. The operators are very supportive and thankful for the help you can provide, and the more information they get, the quicker it can be resolved :-)