Touch LCD with Mac Mini
This might help...  when using a trackpad on a MacBook, tapping does not, by default, click the mouse...   there is a setting (System Preferences -> Trackpad -> Tap to click) that must be enabled.   

You might try checking for that...  or something similar, to enable "tap to click" for the monitor (if possible).   I can't say 100% this will work, as I've never seen a touch screen used with a Mac... however hopefully this helps.