Audible Change Signals the End

[penguins21]

I have a computer I'm working on, one of those "super-special" Alienware boxes. It runs along just fine, but then after a while there is an audible change in the fan speeds. At this point the machine freezes up every time. I tried another power supply with no change. The processor, RDRAM, video card and math co-proces. were running hot in close proximity, but even after adding another fan right there it still seems to do this... I've never seen anything quite like this. Is the motherboard any good? Any thoughts?

thanks!
-andrew