Get In through the passenger side door/boot/ however else you CAN get in, take off the door fascia panels, which will give you access to the inards of the door( possibly through a thin layer of plastic which seals the inside of the door- its technically useless but just cut it accross the top with enough plastic to spare to stick it back up with tape if you really really want to )you will see the door lock mechanism and it is connected to the lock up-down switch with a bent steel rod, usually it is just a matter of re-connecting the rod correctly(you can see pretty easily where it goes once you are inside) this silly little rod can still activate locking if its popped out, but it won't allow opening or it just wont respond either way (great huh :) it will lock but not open) if you cant figure out how to connect it, do the same stripdown on the passenger door and look there( i know its hassle but meh :D ) if your car is central locking then it may also be a solenoid (the little bar that pokes through the door frame into the car frame and acts like a dead-bolt) if so, you will either need to reconnect the solenoid as it may have come un-attached , or replace said solenoid, its a possibilty that it will be a solenoid, but more likely the fore-mentioned issue. hope this helps.
--Paul--
Paul Saunders, May 2008