You can add the standard Gnome menu to your panel until someone can help regarding mintMenu.
Just right click on the panel, select Add to Panel..., then scroll down until you find the entry 'Main Menu'. Select add to panel and you will now have a main menu again (hopefully).
At this point, you might try using the Package Manager, removing mintMenu, logout (or reboot if you prefer), then use the Package Manager again to reinstall mintMenu. I looked to see if there might be a .config file for mintMneu we could delete, but I could not find one in the .config folder or in the .linuxmint folder.
Be advised I could be wrong and my advice might cause Mint to eat kittens, etc. I do not think it will, but I give you fair warning....I have not tried this out myself, Might work, should not break anything, but you never know....
All progress requires change, but not all change is progress.
--Henry Steele Commager
...there are some...who use change to promote their careers. And then there are those...who use their careers to promote change.