Nissan Almera door not locking?

Hi, my Almera won't lock or unlock from the drivers door, the key won't even turn. I have to do it from the passenger side. Have tried spraying with WD40, but nothing..

Does anyone know what might be causing it and how I might fix it? I really can't afford to take it to the garage and used to have the same problem with the passenger side and am worried they will both go and I won't be able to get in at all!

Thanks