As i said, mIRC does not recognize links, when mouse over, the mouse pointer don't change
This seems to indicate that you are using the on hotlink event in one of your script to handle the hotlinking yourself, and a bad script can quickly result in you not being able to open link anymore. Try typing /remote off in mIRC to disable all your scripts and see if you can click on url then, type /remote on to enable your scripts back

Looking for a good help channel about mIRC? Check #mircscripting @ irc.swiftirc.net