Can any experts help me?

Basically I am trying to do a temperature sensor that when it sense certain range of temperature, and it will auto activate 4 PC fan(of any power). I and my friend have got one simple temperature sensor circuit but our teacher say that it is useless and now we in despair. So can any pros can help us to solve our problems? thanks

actually the Pc fans works automatically
can u put up the brief circuit diagram,
so that it'l be easy to discuss