Best thing to do is to contact your ISP and see if they have you firewalled or have some sort of block on port 6667. The fact you could connect via 6665 is weird. Tried resetting your modem again? Have you tried several networks? That error just means mIRC has got fed up with waiting for a connection to be established, and so has given up. It's more of an error telling you why the connection attempt has been stopped, not why you can't connect in the first place.
Regards,
