Fan working full speed only .

Hi , i own a Dell Latitude e6500. It worked pretty well until yesterday when fan stopped working . At Bios menu , under "Thermal Events" i see " Fan1 Stopped working " at the time i opened my laptop today. I don't remember changing anything the previous day or installing anything that may have caused this.

The fan doesn't start at all until the temperature of the CPU reaches 50-60 ( sometimes more) , i'm using CoreTemp to monitor it . When it turns on though , it goes full speed ( i'm guessing) it makes a lot noise and it cools down really fast. If it turns on , it won't turn off again no matter how cold it gets ( well i've only seen it go as low as 20 degrees, Celsius btw )   I opened the case and there was just a little bit of dust so that can't be the problem , i guessed that the temperature sensors aren't working  properly.

Is there any way to fix this? or at least control the speed to dial it down  cause it gets too loud , or shut it down completely ? . If i buy a new fan would that fix the problem?

EDIT : Also softwares like SpeedFan or I8KFANGUI don't work because it seems like they can't detect my fan even when it's on and working.   Well actually I8KFANGUI can be used to force fan to high speed but not turn it off or low speed.