extension socket stopped working?

You don't say what country your are in.

It sounds like you have connected the bell circuit but not the speech circuit. The extensions should daisy chain from the Master socket.

If you are in the UK you should have Blue & White to 2 and White & Blues to 5 with no other wires out of the six connected. Try that then see if you get the phone on the failing extension to ring. If it doesn't connect Orange & White to 3 -or buy a more modern phone.

t
February 2008