What can cause a CPU fan not to increase speed?

[Daylon Rankin]

I'm a bit surprised that an hour of googling didn't solve this one for me, I really didn't think I would have to bother you guys with this.
My desktop computer has worked fine for 4 years, but has been shutting off lately due to its CPU safety maximum temperature being reached. Normally, I can run a stress test to bring the CPU usage to 100% and the temperature never breaks 130 F. But lately, it is reaching the safety temperature of 140 F simply by idling on the desktop. What is odd about this is that the fan speed is not increasing to reduce the CPU temperature. I went through all the normal motions of removing dust and reapplying thermal grease with no improvement.

It is my impression that the fan speed is controlled by the motherboard to regulate the temperature of the CPU, so I checked the bios settings and the fan control settings were all turned on and set to normal settings. After a little fiddling, I reset all bios settings to default just in case, with no improvement.

Got any ideas as to what could cause something like this?

 

[Martin1982]

Strange, is the cpu fan pin in the correct connecter and not in cha_fan?

 

[Daylon Rankin]

Strange, is the cpu fan pin in the correct connecter and not in cha_fan?

It is connected to the 4 pin cpu fan port. The ports haven't changed from the time it worked.

 

[Daylon Rankin]

The answer ultimately was to reset the heck out of the CMOS a half dozen times. I guess some bit of fan-control configuration information got corrupted and messing with it enough eventually fixed it. The fan now increases in speed as the CPU heats up and keeps the temperature from ever hitting the emergency shutoff threshold.