Volvo S70 lock problem?
 

So I went to my car and there's something wrong with my locks. I don't have keyless entry so I normally open it by turning the key twice to unlock all doors. For some reason, only the 2 front doors will only open. I tried using the central locking button on the driver side ane it only opens and closes the passenger door. I tried using the passenger side central locking button and it only opens and closes the passenger door, and occasionally the rear door on the right. Whats wrong with my car? This is a total pain having to manually open every single door to my car. I tried replacing the fuse to the central locking system hoping it would fix it but no help at all.

This is somewhat of a big problem because my passenger door does not have the little knob that shows whether it is locked or not. It's stuck down there in the door panel.