Maria,
In my case since I disabled nested Virtualisation and set DirectX9 I've only had it occur twice in a week. Once after OSX sleep and once when left powered and idle.
However for your info, before that change, re-starting Explorer in task manager would require two repeated attempts and then the desktop and taskbar would re-appear. Parts of the taskbar would work, but the start menu would not open or any other 'modern' part of it like 'settings'. Settings would hang if already open. I can't be sure I always killed explorer first but am sure I tried that at least once. I am willing to do some tests if you require more info.
Last edited: May 20, 2015