What should I do when my dog can't get up?

Dogs usually love food at any point of time. In your if your dog is not eating food ,it might due to aging or the other reason is due to lack of proper physical exercise. At present you might be running after your dog to feed him. But this is not good. Dog himself should come to take his food because that is the right dog behaviour. If you will not give him proper exercise then he will not get tired & will not be able to release his stored energy. So, try it once. Take him outside, give him a long walk, let him run for atleast 45-50 minutes a day. Then see, he himself will come to eat his food.