This happens ALOT, and to the map itself if you alt-tab or use the windows button (switch to desktop). Never do that, the bug will stay and you will have to create a new game and the bug will go away. If it's ONLY the menu, then idk sorry
This happens to me when I minimize or press alt+tab or even windows key, if you did that. thats the reason. if not then update your drivers. Try a program called Driver Scanner (Click here) . it searches for updates and downloads it.