Multi Commander has a serious bug.
If you did a fresh install of Multi Commander and then on the 'Quick Look'n'Feel Setup" Dialog pressed cancel the configuration was not setup correct and Multi Commander was set up in a way that made it unusable.
So download the new updated version today. If you already have Multi Commander installed it will try to update it self.
You can fix the configuration by going to the Menu Configuration and select "Quick Look'n'Feel Setup..." and press Apply on that dialog. This will recreate the missing configuration.