I have a problem. I have just got back from Taranaki to find my main line does not work.

Ok here we go then.
X is the main line. ( I think)
From the splice connectors at 'a' two cables run, one to 3 and another to 1. From 1 another cable runs to 2.
From the splice connectors at 'b' one cable runs to 3, it does NOT connect to the phone, instead it goes through the wall to 4.
Phone 4 works fine. As does (5) which is not shown but is on the same line from 'b'.
All of the lines with a cirlce on them are coloured blue and blue white. The ones with the double lines are orange and orange white.
The problem, is that phone number one does not work. Whenever you plug in a standard non-powered phone it is dead. When you plug in a cordless that is mains powered, it sounds as if you are on speakerphone. The phone use to ring, but only every second ring comes through. Whenever you answered it you got the same speakerphone "hall" sounds with occasional crackle.
NOW, nothing rings on line X.
I am assuming that X has fallen out of the splice connectors at 'a'. Is this possible? The cable on X is greasy, would it be greasy if it was never connected? or has been un-connected for the last two years.
Also, would TCL techs use a black cable sheath, with the pairs of blue and orange wires inside of it? If so then it sounds more like the cable has come loose.
I am happy to repair this myself, though I am not too sure what I am doing. (Obviously)