Sounds like the door lock actuator is bad.  It could though just be a
mechanical blockage.  If so, put some graphite powder on the key and turn
it back and forth about 20 times to see if it loosens up.  The door lock
actuator's fail fairly frequently though.  That would be my bet.  It's
about 50 bucks or so.  Good luck.

The central locking on the driver's door comprises both a motor and a
switch operated by the key (as does the passenger door). The switch output
goes to a controller which operates all the lock motors. It could be the
switch that's faulty, or the wiring, or the controller (unlikely). Sorry
to be vague, but as with all electrics it needs logical fault finding. But
my bet would be the switch since its heavily used on the driver's side if
you haven't got remote locking.

I don't know the unit on your car. On some the motor and switch are
combined, some are separate. I'd access the unit by removing the door
panel and bridge the switch momentarily with a bit of wire. If you can get
the locking to work normally doing this then it's the switch.