I have the following passes checked:
AO
Mist
Zdepth
Object Index
Material Index
But when the render finishes all of the passes except zdepth and mist are either pure black or pure white, can anyone help?
No, not without knowing how you’ve set the scene, material and object indices and are you viewing them properly. If you checked those in UV/Image editor, Z should be pure white or if it’s not, it means the scene scale is very small or there is something blocking the camera.
Full resolution screenshots of the blender window and preferably the .blend file in the starting post would speed things up.
For the Object/Material Index outputs you’d usually connect them to an ID Mask node so you can select which index you want to use.
As said above, supply a .blend file or we’re just wasting our time.
Add a Normalize after the Z-depth and route it to a viewer to see the Z-pass. Or adjust the clipping near and far for the camera to avoid an all white pass.