How can I fix my Ford KA central locking?

I have just bought a 1988 1.3 Ford KA and the central locking is all screwed up.
Both doors open from the inside. Neither door opens from the outside. I only have basic key without push buttons. The key works perfectly in the ignition but cannot lock or unlock either door with the key.
How can I disable the central locking?

LESRANN
April 2011