Try these:
/ignore -l -> if it gives output, see if you block actions from the people you're talking to or just type /ignore off
/!remote off -> disables all scripting, so on ACTION events aren't called and not halted either.
Go to colors menu (alt-k) and make sure you can read
Action text right under
Appearance. If you cannot see it, click there anyway and select a new visible colour from one of the 16 coloured boxes below.
Check it yourself, type /server -m, connect to your channel again and type /me testing. If you see that, those other people weren't sending any actions and telling you they did.
If that doesn't work, go to
http://www.mirc.com/get.html and download mIRC again, and install it to a new folder.