I think I figured out how to prevent a "end turn crash". It appeared that the computer was in some kind of memory loop, so before clicking end turn, I saved the game and exited. Then I when into control panel, system, advanced, performance, settings, advanced, virtual settings. Change the memory to the highest setting you can handle (mine is at 9216). This has eliminated 99% of my end turn crashes. Also, it seems to help if you hir ESC a few times after ckicking end turn.