06 Colorado 4x4

Had truck in four wheel drive in the middle of a blizzard. Parked truck and suddenly the odometer is reading svc 4wd. It drops out of four-wheel and it will not engage. We parked the truck in the garage to melt snow and ice and there's nothing left to melt and it still will not go into four-wheel drive. Any ideas I am pretty good with cars but have no idea where to start with this truck.