if at all this problem is caused by running mIRC ... what you can do is download the latest mirc from here , uninstall the current one you are using and do a clean new install of the lastest version..
make sure you are not running any scripts/addons ..
if the problem persists with the new install of the clean mirc without any scripts then i am sure its not the mirc , has to be something else ,
still if you are not satisfied ... check with the bugg report section fo the Message Board ...
and may God not rain in london today ...