most likely one of three things-either no power to the fan motor,faulty relay or the temperature sensor(for the fan,not the temp. gauge)is faulty.-have you actually physically measured the engine temp?-the gauge could be reading incorrectly,as a quick fix you may be able to 'hot wire' the fan from a switched pwr source.. hope this helps
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.