how can i fix my ford focus estate W 2000 reg 1.6 16v?

There is no connection between my remote key fob and the car, I have tried changing battery in key no change, programmed key to car (bleep on radio) no change, the central locking and deadlock is working manualy with the spare key, but driver and passenger doors lock with the fob key but will not open with the fob key (i thought this mite be down to ware on the fob key but why would the key work one way and not the other, lock but not unlock) please can you help me with my problem.