mIRC is the client/program that you use to connect to an IRC network. The only way that I can see mIRC being down, is if your computer is also down.
If you are trying different servers that all go to the same network, and that network is down, then you still won't be able to connect. If you are trying to connect to the Karaoke-Realm network, as referenced earlier in this topic, and discussed in another topic, it appears that they didn't renew their agreement with their hosting site, thus it has lapsed/expired.
If you are referring to another network, please specify which network you are trying to connect to.