STOPPED EATING HIS FOOD

I HAVE A MINATURE SCHNAUZER 9 MONTHS OLD AND VERY VERY CLEVER.
HE NORMALLY HAS DRIED DOG FOOD AND HAS STARTED TO TURN HIS NOSE UP AT IT. WE HAVE TRIED OTHER DOG FOODS BUT HE IS STILL NOT WANTING TO EAT.
HOWEVER IF I HAND FEED HIM THE DRIED FOOOD OR THROW IT ON THE KITCHEN FLOOR LIKE A GAME HE WILL EAT IT.
I AM AT A LOSS OF WHAT TO DO. HOPE YOU CAN HELP.