I was playing a game when suddenly, my screen went black.  Hitting the ESC key did not bring-up a menu so I could not save the game or exit gracefully.  The screen snapshot below shows Task Manager in the foreground and GalCiv4 (black) in the background.  Task Manager shows that GalCiv4 is using about 20% of CPU so it is running and doing something.  The only thing I could do is kill the GalCiv4 process.  When I reloaded the last Auto Save it did not happen again.

I realize that this does not help you fix the problem, but it does make you aware that there is a problem.