Hi marlnet,
Thanks for choosing The Events Calendar!
FIrst off, you will need to have The Events Calendar (which is what I assume you mean by Free EV) plugin activated to use the Events Calendar PRO (ProEV?). PRO simply adds additional features to The Events Calendar.
As far as the styling goes I’m not sure what goes “horribly wrong.” Could you provide a screenshot by chance?
One thing to perhaps try in the mean time is to switch out the Default Stylesheets under the Events > Settings > Display tab. Do any of those make any difference?
— Julie