Check that the sensor is working. Print out the analogRead value, without any calculations. It should be about 40 in a 20 degree C environment. If ARef = 5v.
Serial.println( analogRead( tempPin ));
If that is reasonable then this should give you the temperature in degrees C.
float DegreesC = ( AnalogReadValue / 1024.0 ) * 500.0;
If it is not reasonable either the sensor is defective or your wiring is wrong.