fiesta not starting, not even turning over?

Depending on the year! the immobilizer will not stop the starter motor from turning it just stops the signal to the fuel pump , the injector/s and the ignition coil, if it's an automatic the start inhibit relay will stop the starter motor, but if a manual your looking at either a faulty starter motor or the ignition switch

nigel
March 2009

You dont mention the year or model.
Two trains of thought on this, yes it could be your imobiliser.
Or if its an older model and been round the block a few times, the Starter soleniod.
First off i'd check out the soleniod and all wiring to go with it, it could be just a filthy terminal

Colin
March 2009