If you can still get to the Immediate Window for code (press Ctrl-G), then you can type this in to perhaps get everything back to normal:
CurrentDb.Properties("AllowFullMenus") = True
CurrentDb.Properties("AllowShortcutMenus") = True
CurrentDb.Properties("AllowBuiltInToolbars") = True
(You can just copy/paste that in to the immediate window, but make sure you press return after each line.)
Save the DB, close it, and open it, and you should have full menus again. That code is the equivalent of going to Tools -> Startup and checking the three checkboxes with the names given above.