1997 Cadillac STS

It is a bit more difficult than it sounds. What you are likely to have is a failed ignition cylinder, the wires up near the rotating portion of the cylinder eventually give up. There are two ways to go about it. One is replace the cylinder with new keys, the original key value can be obtained by vin, or a tool called a VATS interrogator. The second option is to bridge the harness side of the connector(at the base of the column) with a resistor pack that is the same(or very close to) as they current key resistance value. What you are doing by this, is substituting the pellet in your key. The only pitfall to the second option, is the car can be started with anything that can rotate the cylinder. You could even place a new cylinder, connected with a key in it, under the dash to act as your bridge, and accomplish the same as the resistor pack.

I don't know what he could have done under the dash, and I am not familiar with a VATS chip. By someone saying the computer is shot, you have somewhere in the neighborhood of 15 computers on that vehicle. The ignition cylinder is a simple test. With the large connector at the base of the column disconnected. Place an ohmmeter across the two white wires that are in an orange conduit, on the column side. You should have open circuit. Insert your key, you should have resistance close to the pellet value. Rotate the cylinder through all ranges, off, run, start, and it should have the same resistance value at all times. If it cranks, fires, and then dies, it probably is not the cylinder. Press off and passenger warmer on your climate panel to enter diagnostics. Record all the codes that display, particularily PCM, and VTD codes. It should display all codes after a brief segment check.