on the focus as well as most other ford products all you need to do is put the cars ignition in the run position, The position that the car is in when running only do not start the engine. Then look under neath the steering column to find a small hole approx 3/16th diameter. Insert a stiff wire or small alan wrench until you feel slight resistance then push harder it will advance only 1/8" to 3/16" then pull on the key.. This will remove the lock cylinder. Now hold the lock cylinder in your hand and rotate the key if it works then the switch mech is being stopped by foreign debris that must be cleaned by removing the switch mech and repair or replace it.
Incidentally I am a ford certified tech.