If it is an immobiliser issue with a chipped key used on the car from which the ecu came, then it won't work without the correct key being recognised, they do usually turn over but no sparks and no fuelling.
It may be this, need to look at key on other car, or for a ring around the ignition switch used for detecting the code of the key where used.
If not this it may be just something you've missed connection wise.
tabetha