I have been a Multi-Edit user for 20 years and have never encountered this problem. A co-worker new to ME tried to edit the Main menu, got lost in the edit dialog, pressed a wrong button, and both the main menu and toolbar vanished.
What she is left with is nothing but an empty window with the ME logo at the top. She is unable to do anything except load a file. The keyboard shortcuts to activate the drop downs for the menu do nothing. Her ME installation is functionally useless and completely unusable.
I have googled the problem, searched extensively through ME Help, and have found no information on how to make the Main menu (or any menu) reappear. Unless one of you can help, it appears our next step may be to uninstall/re-install ME.
At this point the only option would be to restore to the factory defaults. Use the following post to locate your config directory. Then with Multi-Edit (ME) not running, delete meconfig.db and wcmdmap.db. When you restart ME it will load the "factory" image of those files.