Unfortunately Balls can stop eating for a lengthy period of time and for a variety of reasons. There are a number of tricks to get them to start eating, but nothing is guaranteed. Quite often the only thing you can do is wait it out and keep offering food.

First off, what has your snake been eating? F/T or live mice or rats? It's a good idea to offer food just after dusk when they are usually in feeding mode. Pre-scent around the cage by placing the prey item near the cage for 20 minutes, then offer it to the snake. If it shows interest, try to get it to strike by wiggling it but don't do it so much that it scares your snake.

If you're feeding live, you can pre-scent the area by placing it in a paper bag and putting it by the snakes cage. I would recommend getting a large rat pup and keeping it in the cage overnight. I wouldn't suggest going larger than a weaned rat or small mouse as they might start chewing on your snake.

Many people have also had great success by offering ASF rats (African Soft Furred). They are the Ball Pythons natural food, and many picky eaters will strike those without hesitation. The only problem with that is that your snake may get imprinted on ASF rats so you will need to continue feeding them.

Make sure that the snakes environment is perfect as far as temps, humidity, adequate hides, etc. This will reduce stress and encourage your snake to eat. Also, try not to handle your snake at all until he begins to eat as handling will only increase its stress.

Good luck!