After hours and hours of building my city, the game crashes back to the desktop every 5 minutes or so.  There is no error message, no warning it just closes the game.
I have plenty of ram, a brand new HD video card that has updated drivers.  I have installed every patch I could find on the net for SC4.  
I have tried uninstalling and reinstalling the game 100 times.  It happens only when the game is moving.  If it paused for an hour while I build something it never happens.
I am at an utter loss on how to stop the crashing.
I have even tried what a lot of you suggested and turned off one of the processors while I run the game.  Still crashes.  
I am using Windows XP Service Pack 3
Please help me!