My wont start it says starter disabled and thief system

You have GM's VATS security system. Most likely in this situation the problem is going to be the ignition lock cylinder. Inside of the lock cylinder is two tiny wires that come in contact with the pellet on your ignition key. Over time the wires break off and the computer thinks the vehicle is trying to be started without the ignition key. To confirm this you need to measure the resistance value of the chip on the key pellet. Then, at the base of the steering column, unplug the ignition lock cylinder connector. With the key in the ignition lock measure the resistance value across the two wires. It should match the reading you got from the ignition key pellet. If you get no reading, or a different reading across the two wires, the bad lock cylinder is confirmed. The new lock will come with a template for cutting new VATS ignition keys. You can use the chart below to determine which key you need. There were 15 possibilities. Hope that helps! Jim