Q: Vehicle starts then immediately dies (injectors cut out).

My 2004 Denali is not starting properly. The car has started and driven fine in the past with no issues. A few days ago I removed the battery to splice in a new seat connector that had shorted out. Today, after putting the seats and battery back in, the car will not run.

With the key in ON the DIC does not light up. The engine cranks and starts but then immediately dies. It seems as though the injectors are being cut off by the security system.

After the car dies, the DIC lights up saying "unknown driver" rather than "driver 1". Following this, the security light illuminates for 1-2 seconds then turns off.

Why is the car not recognizing the key? How do I make it recognize the key and start again? I have performed a security reset by cranking the key, leaving it for 10 minutes, turning it off few seconds and repeating twice but it did not reset the passcode. I am at a total loss...please help!

My car has 180000 miles.
My car has an automatic transmission.