I have the same atv.it has a "demand 4" awd.Which means the rear tires have to spin without traction before the front wheels will engage.A good way to test it is lift the rear end up on a block of wood to suspend the tires.Put it in awd mode and gas it.The front tires should pull the atv off the wood.
It be the both cases of one of them. You should take it to a mechanic.
You should have a couple wires running to the front differential with a quick connect plug, check this plug to see if it has come apart or the wires were broken somewhere.
that is the most common problem with belt driven macines you may have a bad seal or crack in your belt cover