When I try to start my car it says, "starter disabled due to theft system..." on 1990 Cadillac Seville

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Starter disabled due to theft system, wait 3 min, 2 min, 1 min, start car. But it won't start and the computer repeats the message. What is causing this and what is the cheapest/fastest solution?
(2) Answers
Vehicle Application: 1990 Cadillac Seville 4.5L

Customer Concern: The computer is shutting off the fuel injectors. Gets one pulse and nothing after that. The engine cranks fine. Has spark. Put a Passkey decoder module in it and there was no change.
Tests/Procedures: 1. At the Passkey decoder module, the Dark Blue wire should be about 2.5 volts with the key on.

2. If not, ohm test the pellet on the ignition key and note the reading. Next, with the key in the ignition, disconnect the Passkey module and ohm across the Purple/White wire and the White/Black wire, it should read the same as the key pellet and stay the same as the key is rotated to start. If not, verify that the wires to the column are OK. If so, replace the lock cylinder assembly.

3. If the ohms are the same, verify that there is good power and ground to the module even with the starter engaged and the Blue wire has 5 volts (from the engine computer) with the Passkey module disconnected.

4. If all OK, replace the Passkey module.
Potential Causes: Ground
Lock Cylinder
Powertrain Control Module (PCM)

Tech Tips: Bring the old key to the dealer when getting a new lock cylinder, so the proper pellet will be used in the new key.
The most common problem is one or both wires broke from the lock cylinder to the decoder module.
do you have any idea