I have installed a few of these and once you do one or so it becomes pretty easy. I have installed them in existing homes and that is tough. If you do one in an existing home be sure to check the trusses there is no doubt you will have to fabricate a few things but it can be done.
I can tell you a few things about them. First if it is not working it is either the limit switch (like Fred said) or the breaker for the motor circuit. If it has been working for a few years it can only be a couple things. The limit switch is located above the octagon box and below the pully system. All the ones I have installed (back three yrs or so) have an extra limit switch right next to the one in use. Just change the wires from one to the other. There should only be one switch in operation for the system because there is a low voltage key switch to bring it down so you limit the lowering yourself.
There should be two wiring methods to this system. One being the motor and the other coming from the chandelier swithc itself. My guess it is either the limit or the motor breaker.
Hope this helps. Good Luck.
By the way be prepared to stand on your head to do the limit switch. I would take up a flashlight, a pair of Kleins, and a screwdriver, with a tester. should be all you need. I is going to be in a very poor location for you.