It won't start, if there's an immobiliser issue.
Somewhere along the line, the key transponder, the antenna that reads the signal and the BCM (where the immobilisor chip lives) have got out of sequence.
If the car battery went very flat recently, that may have corrupted the last stored code in the immobiliser; it would need to be re-synchronised with the key.
It's more likely that the antenna isn't reading the key.. so have a look at that. It lives next to the ignition key barrel and is connected to the car via its own plug (yellow or green rings a bell).
It may just need re-connecting/cleanly or it may be damaged.. but they should be easy to find second-hand.
Ralf S.
