2000 Cadillac El Dorado Car will not start

More than likely, it is a fault in the vehicle theft system. The ignition cylinder is a common culprit. There are small wires that come up the steering column to the contacts that read the key pellet, these break over time and use. If you check resistance on these leads at the base of the column with the key inserted, and you get O.L., you need a cylinder.