Rather than cut and pasting all your other files (aliases.ini, mirc.ini), into your mIRC folder, actually cut and paste your mIRC.exe into your old folder.

There is an option about keeping your old scripts when you downloaded mIRC, but since you passed that, might as well do the above.

So if you have an old mIRC folder (with no mIRC in it), and a new mIRC folder (with mIRC in it), cut and paste that mIRC from the new folder to the old.