What could be wrong with my turn signals?

I have a 2002 chevy Malibu SL. My turn signals will sometimes not work. At times it will blink and click a couple of time then turn off or not turn on at all. The signal doesn't even come on the dash board when this happens. I have fun when the car is somewhat cool it seems to work just fine but on a really hot day or if my car was in the sun and is warm the turn signals won't work