Ford Focus Central locking issues?

Hi,

I have a 99 reg 1.9l Ford Focus LX,
My central locking has just died! The remote control does not work, the boot release button does not work and i am unable to lock the back two doors. i need to open the boot and front doors with the key.

I have replaced the fuse on the back of the fuse box (63 i think) several times during the last coulple of years, although it was blew, this did not fix my problem. when i did this the central locking system tried to work, but sounded like it was struggling and immediatly re-oppened. It done this a few times before eventually stopping (i guess the fuse blew again)

Any clues as to what is going wrong?