First and foremost, I have looked for solutions to this for some time now, here on the mIRC boards, and on other sources. I've configured my router to allow all the ports mIRC uses, including 6667-6669, and 113, with no luck. I've enabled the ports necessary, and then disabled the Windows Firewall as well.
Oddly enough, another computer on my network, behind the same router, can connect with no problem.

No server/network combination seems to work with mIRC. I've reinstalled the client several times as well.

I'm out of ideas. Any help?

Which computer is the main one on the network? The one that works, or the one that doesn't?

The one that doesn't.

Well, I have limited knowledge of routers because I never use them, but....

From what I have heard, I believe that when you forward ports between computers on a network, you need to allow both computers to use those ports (and depending how you set it up, that can sometimes not work because you can't have the same port forwarded to two locations at once). My guess is that your ports are forwarded to the other computer and not the main computer.

Maybe someone with more router knowledge can give more information.

After I write this I'll try completely bypassing the router, and hooking directly to the modem, and that should definitively say whether or not the router is the cause of the problem.

The ports that are forwarded are being forwarded to this machine (the one that cannot connect), and there aren't any ports forwarded to the computer that doesn't have connection problems. I've also gone a step further and tested running this machine in the router's DMZ, also to no avail.

*Edit*

It is the router. I bypassed it and connected to different servers and networks with no problem. I've got one last-ditch idea, and I'm going to restore my router to factory settings, and then update its firmware.

*Edit x2*

Well, I reset the router to factory settings, updated firmware, and reenabled the ports. I don't know what exactly changed, but I can use IRC chat now. Thanks for the help though.