Does not start

Hello,

Just to clarify, the vehicle will start as normal, but once in a while it will not start, right?

When it does not start, what do you experience?
Does it make any noise? Any clicking?
Do the dash lights come on?

Please let me know little bit more information.
Thank you.

https://www.2carpros.com/articles/car-cranks-but-wont-start
https://www.2carpros.com/articles/starter-not-working-repair

Everything still comes on like normal, dashboard lights and radio. It doesn't make any noise. There is a clicking sound when I turn the ignition off again

Hope this helps a bit.

It sounds like an intermittent issue with the ignition switch. The ignition switch is the electrical component that the lock cylinder mounts to. It has several connectors and pins and over time due to wear and tear it can malfunction and can trigger this type of issues.
Since the Fiesta was not available in the USA in 2006, I am unable to provide the replacement instructions for the switch.
But the switch typically requires removal of the steering wheel.