phat

i had it in 4h driving on it for a day, was parked in a parking space reverse out in snow all of a sudden i hear a "clunk" sound. have driving on the street for a bit i tried to switch back to 2h will not go back. parked the car for a hour turned the truck on switched it back to 2h then hear gears grinding and it went back to 2h from 4h. from this point on the 4h or the 4l will not engaged. please help!!!!!