Spectrum landline has no dial tone when plugged into house network
We just switched from Vonage to Spectrum landline. Under Vonage we were able to use the existing house network by back feeding the connection into a phone jack. This also worked for a few days after the Spectrum landline was installed. But suddenly it quit working. I can get a dial tone now only by plugging a handset into the Spectrum modem. When plug the modem into the house network the dial tone goes away (i.e. a handset plugged into the house is silent. Currently, I have unplugged all of the handsets, except for the one I use for troubleshooting.)
Since it worked OK for a few days I assume that something changed in the network, causing this problem.
I did some troubleshooting with the handset and found that the dial tone could be heard at the house punch down block (66) input line, but only if all premise connections are disconnected. With the dial tone disconnected the premise line 1 pair seems to be open, no short circuits or voltage lurking. There are 13 jacks in our 6-bedroom house, so I have not tried each one separately. But first I would like to know if there are any restrictions or conditions that I may have overlooked.
As I said above, there are 13 jacks in the house, with 13 gray cat5e cables going to the 66 block. But there is one more cable, a blue one, also connected in series making a total of 14 ports on the board. Does anyone know what that might be? [It's not the alarm, which is yet another white cable going from the alarm's RJ-31x biscuit to another section of the 66 board, which I have temporarily disconnected.
I'm thinking I may have to unwire the premise Line 1, find the bad connection, and rewire all of the premise wiring, a task I would like to avoid, because I don't have any pushdown tools and have never done this before.
Does anyone have any ideas what may be going on, or perhaps a less drastic method of finding the bad wires?