What exactly happens? How and when does the mobo shutdown?
Try using a single ram card at first.
What happens is when I hit shutdown in the Windows Start Menu the computer will display the shutting down screen and then the screen will go black but the fans and LEDs are all still powered.
I have heard of other people with this problem and have had success with various solutions but none of these work for me.
There must be some program that is preventing the shutdown process to complete successfully. Turn off unwanted apps in msconfig one by one and see if that fixes your problem. Just remember not to disable any windows service.