Hello and thank you for using Just AnswerI'm Paul and I will help you with your Question
when the security light blinks this is because the computer is have a problem reading the ignition key through the passlock sensor.
you can attempt a relearn of the passlock by turning the key to the crank position for one second. then release to the run (on) position
leave the key in the on position for 12 minutes
the theft light should go out.
once the theft light goes out try and start the vehicle. if it does not start on first try turn key to off and then retry.
you may need to repeat the 12 minute procedure up to 3 times to get it to relearn
if it will not relearn you will need to replace the passlock sensor
let me know how you make out and if you need more help