My dog is a German Shepard pup and he will not eat at all what should I do?

How old is he,

The vet recommends frying up lean ground beef drain, rinse, drain, and set aside.
Boil up rice---wheat is better but plain will do. Mix the rice with the beef.
Serve the dog 1/2 his normal ration of dog food and top up with rice mixture.
Slowly gradually wean back the rice and top up with the dog food.
Eventually you will be back to dog food only.