I have a Gateway desktop that was purchased about 18 months ago. It has started shutting down without warning over the past week or so.
I installed Speed Fan (4.42) and ran some simple measurements.
My CPU temp was getting > 110 deg C during heavy useage (long periods of Flash playback)
I compared the speed fan reading to the reading in the bios and it is close, so I think that its reflecting the truth of the bios reading.
I measured the cpu temp with a digital meat thermometer by measuing the temperature of the thin metal blades installed beneath the CPU fan. The blade temps were about 20 deg C lower than the bios reading. When I did this I did notice that all the fans were spinning and I cleaned out all the dust.
I am assuming that the high core temperature is what is causing the PC to shut down.
Its funny that I am having the same issues with my PC shutting down due to over-heating these past few days out of nowhere, and this is AFTER I cleaned the heatsink and re-seated it to give it better air flow. I am going to buy some thermal paste later today and re-adjust to see if that helps. PC was running with 8 gigs of RAM/SWTOR MMO and at around 120 degree F before it shut down.