1997 Cadillac DeVille, was not started for 2 Years and when I charged the battery the car would not crank. On the Dash It states "Theft System Problem" & the Remote dose not unlock or lock the

SOURCE: 1997 cadillac deville anti theft

This might work for most:

Theft Module Re-learn Procedure without a T5O or T6O
During this procedure, the vehicle battery must maintain a minimum of 10.5 volts. If the battery is not fully charged or is weak, a battery charger may be connected.
NOTE The battery charger must NOT be set in 12 volt boost. This will prevent this procedure from working.
1. Cycle the ignition switch to the "Run" position.
2. Wait a minimum of 10 minutes, cycle the ignition switch to the "Off" position.
3. Cycle the ignition switch to the "Run" position.
4. Wait a minimum of 10 minutes, cycle the ignition switch to the "Off" position.
5. Cycle the ignition switch to the "Run" position.
6. Wait a minimum of 10 minutes, cycle the ignition switch to the "Off" position.
7. Verify the repair.

and if not try this:

STARTING DISABLED/DUE TO THEFT SYSTEM/REMOVE IGNITION KEY"
If the Powertrain Control Module (PCM) does not receive the Fuel Enable message it will use the class 2 serial data line (CKT 1807) to tell the Instrument Panel Cluster (IPC) to display the "STARTING DISABLED/DUE TO THEFT SYSTEM/REMOVE IGNITION KEY" message on the Driver Information Center (DIC) . This will inform the driver of why the engine is not starting. When the ignition is turned "OFF", the IPC will start a timer and display messages to inform the driver to wait for the PASS-Key II timer to run out. The messages will read "WAIT 3 MINUTES", "WAIT 2 MINUTES" (after 1 minutes has passed), "WAIT 1 MINUTE", and "START CAR".
If the timer was not run out, the IPC will not send the Fuel Enable message. When the PCM does not receive the Fuel Enable message, it will command the IPC to re-start the message process.
This message is most likely caused by an improper key resistor value or the IPC did not properly sense the ignition key resistance.
good luck!

SOURCE: 1997 cadillac concourde deville, car wont start

Try to reset the p.c. by unpluging the batt. for 10 min that should do the trick.

SOURCE: 2001 Cadillac Deville Security System

I had a similar problem intermittent NO START. No click, buzz or other noise. Everything worked but wouldn't start. Unfortunately it took two trips to the dealer to locate the problem. Next time it happens find the purple wire in the wire harness under the cover on top of the engine. A simple tester that connects to ground with an lighted "awl" type probe will tell you if there is power from the key to that point. If there is and you're not starting then the only other thing downline is the starter. Can't repair them only replace. Dealer will be about 900.00 P&L , If you're daring or have some help it's right on top DIY 400.00.

SOURCE: 2001 cadillac deville theft lock on after replaced battery help!

IF when you purchased your car you didn't set your own personal code you will have to take this to your local GM dealer and they can pull the code that is set at the factory and unlock your radio.THe proceedure for setting your own code then unlocking radio is in your owners manual.The dealership I worked for did this for free.

SOURCE: '97 Cadllac Deville Concours reading "Anti Theft System Problem"

I had the same problem. trying to save money i took it to several auto places who thought they could fix it..... after a lot of money and my 800.00 after market alarm was taken off i had it took to the dealer . They fix it in two hours they put in new switch and key haven't had any problems sence.