Have you checked if mIRC could obtain your real (external) IP address after typing /localinfo -u ?
If you are connected to a server that masks you host/IP address, this command may not work. It's because some servers don't send a user's real host/IP even to the user himself.
As you are on a dsl connection, /localinfo -h won't work either.
The only thing that comes to my mind is learning your real/external IP address and manually entering it into mIRC Options, Connect >> Local Info