I have a 03' ford courier, i lost the key and have got a new key cut. how do i byp the immobiliser?

the alarm is a "sentry" brand of alarm. is it possible that the original key was coded in some way? could i get an auto electrician to remove the immobiliser? the new key can turn the alarm off by unlocking the door twice. it fits perfectly and turns the ignition on, the glow plug light shows then once i try to start it, the motor turns over but wont fire!! any help would be greatly appreciated.