Yep sounds like the battery. My focus did this, and I thought that water had got in the fuse box or something because of the electrical ticking, a quick call to my local ford garage confirmed it was the batt.
Even though the lights, wipers and radio all still worked, they said, if the battery goes under a certain level, the car will not start up.

Sounds just like the problem I had. I don't know if the fiestas will do it but on the focuses or foci when you start the ignition the RMP and odometer needles will go up to their maximum and then back down. I would expect that it may not happen on yours as I don't think fiesta instrument clusters are quite as digitalised as the focuses.