Hi!
I'm having the exact same issue as JohnOZ. When the PC needs the fan to increase the speed, it simply shuts down or runs at a very low speed, causing the CPU and Motherboard temperatures to reach over 90ºC, making it impossible to use the PC.
I have the latest BIOS upgrade, no dust nor any signs of it, no damaged parts from falling or similar things. The same failure message is displayed at restart. And the fan only starts running again if I shut down the PC and wait for it to cool down.
I have an HP Pavilion dv-6180sp, with less than 2 years. The heating has always been a problem on this PC but never over 80ºC