It's not you, I had this same problem.
For me the problem is the Ozone 7 installer assumes you will install it to C:\Program Files (x86)\iZotope\Ozone 7 if you don't all sorts of bad things happen. I contacted them within a few hours of Ozone 7's release about their problems with the software assuming this and they admitted it was wrong but obviously haven't bothered to update it or fix it.
For the MP3 preview problem the plugin attempts to load
C:\Program Files (x86)\iZotope\Ozone 7\win64\libmp3lame.dll and when it fails rather than tell you, it just causes the MP3 preview to not work.
In my case I had installed Ozone to d:\Apps\iZotope\Ozone 7 (I don't put things in c:\Program Files or c:\Program Files (x86) if I have a choice)
In order to fix the MP3 preview I just made a copy of the binary files in d:\Apps\iZotope\Ozone 7 into C:\Program Files (x86)\iZotope\Ozone 7 (so the win64 directory with it's copy of the lame DLL) was in the right place. This fixed the MP3 preview for me. I think it may also fix the in-plugin help or something else, can't really remember exactly.
If this is your problem you might want to contact them and complain, clearly they ignored me since Ozone has yet to get any updates or changes.