cranks but does not spark

my vehicle's previous owners have had somebody trying to steel the car and failed leaving the ignition destroyed, so at the time the owners had came across a Nissan Pathfinder same year and swap the whole ignition out and along with ECU that is when i had purchased the vehicle. everything works, but now it just cranks and the anti-theft light blinks stays solid. is this why my vehicle wont start? because i had heck all from drive to park. fuel all good it cranks but does wont start. how do i go about fixing it until I pay a mechanic, but do not want to get charge for more that needs to be done.