The reverse in your sled is PERC (Polaris Electronic Reverse Control.) It works by stalling the engine, and just before it dies, the electronics fire to start the engine to run backwards.
When you push the button, there should be a flashing light in the speedometer. If the light doesn't come on, you could have a bad button. If the blinking light comes on and the engine dies when you try to move, it may be in the wrong mode. There are two modes, one for low elevation, one for high. You can change modes by holding the button in. The speed of the blinking light will change from slow to fast. If it's blinking fast, hold it in and try the slow mode to see if that will help. The fast blinking is the high elevation setting for elevations over 6000 feet.
Directions and explanation of the PERC are on page 63 of the owner's manual. If you don't have one, you can download one from Polaris at http://www.polaris.com/en-us/Company...9918225r03.pdf