Is the little immobiliser lamp on the right hand side of the line of lamps on the dashboard still flashing? If so, your engine is still immobilised and that's why it won't start (you didn't state whether it was still flashing or not). I'm not sure what you mean by "go through its sequence".
If it's the immobiliser, you could try rubbing the key body around the ignition key barrel, flat to the steering column cover, until it goes off. I've had this issue with mine for years until just two days ago I tried a new technique and have had no problems since. I simply put the key in the ignition (with the number and dot towards me) and count to two. The immobiliser light goes out and I'm good to go.
If it's not the immobiliser then it's just a case of going through every usual "car not starting" thing. Good luck.
