First I'm sorry for your loss, it is the worst feeling to lose a pet.
Second you had it for a week and it was eating and drinking fine? Was this based on your personal interaction with it or from what they told you when you bought it? In 1 week I would assume it had maybe eaten once for you, since it should have been given some time to settle in and then eat something? If you are taking the health based on what the seller told you then I'm wondering if you were not sold a potentially ill baby to begin with. Unfortunately there are people out there that sell sickly ch babies and label them healthy feeding established babies and many people don't recognize the signs of an ill baby ball, a friend of mine made the same mistake at a local show recently and after bringing it to me I pointed out that the skin was hanging off her and she appeared to have not eaten in a good while even though he was told they were all eating regularily once a week. He managed to go back and get his money back. Talk to the person that sold it to you, and recheck your set up, heat matts can also malfunction wich could have caused a problem. The only way to know for certain is to have a necropsy done but I would be looking at a previous problem when it dies in only a week.
-----
Nita Hamilton
--------------
Ball Pythons
ballpythonworld.com