My computer turns itself off unexpectedly after some time of use. It appears that this might be temperature related, but not for sure. I installed 2 tools that monitor temperature: SpeedFan and CPU Thermometer. The only definite finding is that there is a sensor (labelled temp1 in SpeedFan and CPU in CPU thermometer), which shows a temperature of 108C a second before the computer powers down. Until that moment, this sensor shows a constant temperature of 40C.

I can usually reproduce the shutdown by viewing a few movies together, which cause another sensor (labelled CPU in SpeedFan) to go up to 60sC, but I do experience the problem even at times when this sensor remains low and cool. It does seem that the problem is more frequent if the computer is turned back on immediately after shutdown, but not always.

I have had other hardware problems recently, which might be related:

1. My hard disk heated up. I installed a fan on it, which worked to reduce the heat. The hard disk sensor shows around 40C.
2. I had occasional blue screens and hard disk failures. Replacing the power supply seems to solve both these issues, but then this powerdown problem began appearing.

I would appreciate any suggestions as to how to determine where the fault is, or what needs to be replaced.