I had a very old PC, Dell optiplex 960 to be exact. i accidentally short circuit the the fan connector after which fan stopped spinning. I check the power and it was cut off so i started powering the fan using a pin(12v) from power supply connector(sata connector). Now the fan is spinning but the system does not detect it always and gives me annoying error each time i boot up. I have checked the rpm connector coming from the fan using multi-meter and it is working fine. Also the system is setting the speed of fan according to the temperature sensor(i actually tested it by heating it up and cooling it down) which means pwm pin is also working fine. The only problem is, it sometimes gives error of CPU fan not found.