Mine's an SE, and with an On Board Computer had a kind of immobiliser - it would turn over but not fire. This is certainly what happened when I took the OBC out in the end I just had to join two green wires.
Unplug battery for a good hour to reset OBC - then charge up and try again maybe? Remember your OBC immobiliser and codes, instruction book etc.
Also check the brushes in your alternator, and also the diode on the back of the alternator . . .I replaces both on my alternator, and it was good as new after
What's the current state of the battery?
Does the engine crank?
Crank and not start?
Disconnecting the battery for half a second will defeat the OBC immobiliser, but you may have a second immobiliser.
Open up the 'phantom' battery terminal on the engine bulkhead, behind the front battery tray, and connect a 12 volt bulb between the smaller terminal and earth, to establish that power is present there.
Connect a piece of wire between this small terminal and the + terminal of the ignition coil, leaving all existing wires in place. Try to start the car.