Sorry to hear that you have not found your short. You should not get any continuity between the white and black wires if all devices are disconnected. If you still have a short it must be in the wire between the electrical devices. Maybe the wire got too hot and melted together or a nail or screw penetrated the wire if you have been hanging pictures or doing some kind of home repair, or the wire was run through some kind of pinch point in the attic and the house settled pinching the wire. What you will need to do is determine where the short is and wire around it. To do this find the "in" wires in each electric box on the circuit, and the "out" wires and seperate them. Check for continuity between the wires in each direction from that point. When you find the first time you show 0 ohms you have found the direction of your short from that point, and that will be the wires that need to be replaced. Good luck.