if the pats light is on constantly and it wont crank, its the keys.
You cant just swap the ecu and then use the keys from the car the ecu came from. But not all is lost.#
Get in touch with an auto locksmith and just get him to reprogramme the keys. its just as if they will be 're matched' to the cars system. Tell him you have keys, they just need programming. I've been called out for this a few times