Central locling help!?

Hi, Could someone help, Just bourght a Fiat Punto Sporting 1997. Central locking had busted. Everything was working ok up untill Friday just gone. I noticed that when i pressed the button on the side on the blue key it struggled to unlock/lock the car. But the light on the key was still working. Any way changed the battery and still not working??? central locking works with the key in the door so i dont think its the fuse? I have tried programming the key as someone mentioned that when you change batterys you need to do this????

Any Help or advice would be much appreciated.

Thanks