Is my system overheating?

the system "idles" just fine. I can cruz the net mostly ok but when I run a prog like Spybot or Win IM or even TRY to run Neverwinter Nights, the CPU fan tools up to top speen and then the sys shuts down. I've checked the CPU fan and blew all the dust out it's spotless. I even have my case open for better ventilation but the same thing. ANY ideas?