Well, it seems that Microsoft has acknowledged a reliability issue on the mobo. Most notably that the CPU bga device loses connectivity of some pads due to rapid temp changes after CPU is turned off resulting from board warpage, so I wonder if adding a cooling fan would only hasten the warpage due to a rapid cooling.
Other questions I have are; Is not that cpu fan rated for 250ma @ 12vdc, how well will it run at 5vdc and how much current will it draw? Secondly, what is the power sequence timing? That is when is 12v de asserted in relation to when 5vdc standby is asserted, and lastly what is the current drive of the standby 5vdc ?
These are issues that I think should be addressed prior to any tinkering or your red button of death, or whatever it is called may occur sooner than if left alone.