Hello, I hope the following is of assistance.
There was a concern with the engine management control module (PCM) not shutting down correctly, the result of this was when you try to start the engine the immobiliser would still remain active, at the time the only repair was to replace the engine management module. I'm not sure if this is still the case or if there is a software update that resolves this issue now. Usually if this is the concern disconnecting the batteries then reconnecting them allows the PCM to reboot and the engine will start.
Obviously there are other issues that can give the same symptoms, check the relays in the fuse box under the bonnet, make sure the terminals are a good fit as I've seen a few of these with a poor connection here.
The main thing to start with is to confirm if the engine immobiliser is remaining on, put the ignition on and wait, if the light comes on for 3 seconds then goes off the immobiliser is OK, if it flashes fast then the immobiliser is still active. If you just get in and turn the key fast the starter motor may turn briefly but will stop again as the immobiliser will still be armed, you just beat it through the self test.
I hope this helps, let me know if I can assist further and I'll reply as soon as I'm able to.