It's weird:

I connect on a server that excists!
I'm waiting and waiting... A half hour...
Finaly! I'm connecting. But then i see "Unable to resolve server"
And when i go on the mIRC from my sister, it works.

What's the problem?

Its a bit like asking the electrician why my car wont start. How about helping us to help you by giving a little more information like network name server name and port?