Ford focas zetec 1.6 51 plate?

I've have done the activating door locks before after my battery needed to be replace. This has been very successful in the past, but now I've had to replace battery again it won't do all of it. I can get the boot and door to open fine, but I can't get it to lock still. It does all the beeps and I've know I've done it correctly bec I've done this before, so I really don't understand why. Can anyone help? Thankyou!!!!