cooling fans don't run

i have a 1995 olds cutlass supreme with a 3.1 in it and it suddenly started to run too hot, the cooling fans do not start. i replaced the sensor that is next to the thermostat, and it didn't help. i purchased the other one that i am told is the one that controls the fans, but cannot find it on the engine. can anyone tell me where it is? or even if this ismy problem?