Theft lights flashing and engine won't turn

Cars work great for the last 8 months since I
bought it from used dealership but this past
month the theft light starts flashing the car
clicks but doesn't want to turn over I tried
the keypad I put in the factory reset code for
the door keyless entry I've locked and
unlocked the door with the keys but still
nothing the last time this happened I got in it
the next morning and it started after a full
day of guessing but now this is been 2 days
do you have any idea why or what this is
doing