One for the tech guys.car transponder/immobilzer problem

[barts96]

help i have lost keys to jeep p-reg

now snapped old lock and have new key and barrel etc

but car won,t run some sort of immobilizer/fuel cut off

starts and cuts out

runs for 2/5 sec then cutts out ,told it has a transponder built into old key which basically sents signal to engine from key and allows car to start

any info please