Latitude E5400 fan issues

I'm experiencing some trouble with my Latitude E5400 notebook fan. At first, i was getting sometimes 100% CPU usage and sudden system restart, with overheating messages - malfunctioning cooling fan, I thought. But sometimes everything just works fine, cooling fan works as expected, and i have no trouble at all.

I started using then I8kfanGUI to monitor the system temperature and fan. When the system starts hanging, I notice the following scenario: CPU goes up to 100%, temperature rises, and I notice the fan is not working - expected behavior from a overheating system. Opening up I8kfanGUI, it shows the fan speed as 10,000 rpm with fans in high speed mode, even though the fan is actually stopped! If i select the option to force the fans to high speed, the fans start, and the CPU temperature drops - but system usage stays at 100%, even with low CPU temperature... and the fan speed still reports as 10,000 rpm.

Waiting the system to cool down and rebooting sometimes solves the problem.

I don't know whether the fan is defective, or maybe de fan controller, or anything else.

Any ideas?