Civ 4 shuts down on vista?

I have windows vista home edition and everytime I start up Civ 4 it plays it normally. After about 5 to ten minutes it shuts down. It doesn't give a warning. The computer simply shuts down. When I restart it doesn't give an error log or even notice that it shut down improperly. The strange thing is that this happens with other games like men of honor but not with empire total war. The computer is not overheating.