Sorry about that.
With out more information I couldn't really speculate as to what's happening... If you're running Windows XP, one thing you might try is looking in the Process tab of the Task Manager (hold down Ctrl-Alt-Del at the same time) to see if a broken copy of mIRC is currently running, and then ending the process if it is. A hard reboot (shutting down the computer) will do the same.
There are also other IRC clients you might have better luck with, like
Klient and
xChat.
