I have a Pentium 4HT 3.0 GHZ processor and a Intel 865 GBL Motherboard with 512DDR 400 MHz RAM, 40 GB hard disk and Nvidia GForce MX 4000 graphic card. The computer turns off by itself without any warning many a times. When I press the power button to turn it off and on again the PC gives an alarming beep and a message during boot screen saying "The CPU was previously shut down due to an thermal event (over heating). Service the machine right away to resolve this." But the fans in my cabinet are working properly and the temperature of my room is also maintained. Nor does any application like Intel Active Monitor shows an alarming temperature raise. The temprature of my computer exceeds to 50 F.