There are two main causes of a snake not eating. One is that it may be getting ready to shed. Do the eyes have a whitish cast to them? Does the skin look transparent in some places? Is he rubbing against any objects in the enclosure? Those are all signs of an approaching shed. If this is what is going on, make sure he has a water bowl big enough to bathe in, and keep the water clean at all times. The shedding process can take up to two weeks. It's normal not to eat during that time.
A snake will also quit eating if it gets too cold. Check your heating
equipment to make sure it is all functioning properly. Check the temperature in the enclosure with a digital probe thermometer. It should be 80 to 85 degrees during the day, 75 or so at night. A separate basking area should be at 90 degrees. Other incorrect conditions can lead to failure to eat, too. Here's a useful site on ball pythons where you can read more about their care and feeding habits: Ball Pythons
You can try different foods - for example, if he always gets mice, you could try a small lizard, such as an anole.
Another reason a snake may not eat is that it is sick. The hard breathing concerns me. Your snake may have a respiratory infection. while ball pythons are known for going long periods without eating, if the snake is actually sick, he could die from that. It's always a good idea to have a vet examine a new pet, but when things start to go wrong, it's even more important. This link will take you to a directory of reptile vets:Vets
As for signs of starvation, the snake would lose weight, the spine may become visible, and lethargy will set in. A bigger danger is dehydration. If the skin around the neck is wrinkled or puckered, the snake is becoming dehydrated. A vet would need to give fluids. If no dehydration is present, you can help prevent it by giving the snake a good soak. Buy some unflavored Pedialyte (yes, the kind for human infants), and prepare a shallow bath consisting of 1/2 water and 1/2 Pedilayte. Soak your snake for about 20 to 30 minutes. Be sure to supervise closely. Snakes can absorb the electrolytes through their vents.
If you have more questions, just let me know by clicking on REPLY. I hope it turns out that your snake is not ill, and that he will soon be eating well.