Try the above suggestions first but it is a very Common problem with the focus and you will need a new ignition cylinder to fix it from happening again. Hitting the key with the palm of your hand sometimes works, but most of the time not. Hopefully the key is turned to and stuck in the "on" not 'crank"position that will make the job a breeze to get the cylinder out. Disconnect the battery so it wont go dead and to avoid accidental air bag deployment if you slip with a screwdriver in hit some wires, remove the steering column cover, 3 screws on the bottom half and the top side should just un-clip from the bottom half, turn the steering wheel so you can see the lock cylinder area clearly, looking at the steering column you should see a small hole with a push pin in it where the lock cylinder goes into the column push the pin in and wiggle the key and pull the cylinder out, the cylinder will ONLY come out in the "on" position.
That's the easy part, go buy a new lock cylinder and take it and the old one to a lock smith so he can assemble it for you. If you have a spare key and are feeling handy you could follow the instructions in the box and build the new one yourself. DON'T get a new lock that comes with keys, your car comes with PATS and you will have to tow it to the dealer to have the new keys programed. I have done 100+ lock cylinders on the focus and the job really sucks if you cant turn the key on.
