since nobody else has ever had this problem and reported it to these forums, i'm inclined to belive its a problem with your PC itself, rather than anything to do with mirc.
Try closing NTVDM.exe by hitting ctrl+alt+del and clicking on it and selecting end process and then running mirc.
It can probably be stopped from running at start up by going to start, run, typing: msconfig and unchecking it in the startup tab.
