Mac mini to cable tv network

Where I live, in my tenant association, we have a cable-tv network. I am a member of the board and responsible for information and communication within our association. We are at present using this cable-tv network to provide an extra information channel to all our tenants.

As I accepted this post I started with throwing out a very old PC and some obsolete software that were used to produce information slides, and replaced it with a Internet connected Mac mini running KeyNote. The result was great. I could update the information from anywhere and KeyNote does a good job. The connection to the cable tv network is through a ordinare video cable.

Everything was just fine, until the day I wanted to use my updated slides from my MacBook Air in that older Mac mini. That old Mac mini had stopped to evolve at Snow Leopard and couldn’t run the latest update of KeyNot, so I wanted to upgrade to another Mac mini I had, capable of running Mountain Lion.

Ans now the troubles starts.

The older Mac mini is connected to the cable tv network with a DVI to video adapter. It have been working great, even if the standard TV resolution isn’t the best. We only connect the video signal, no audio is used. Works fine. Mac mini recognizes the tv output resolution and adapts.

First I tried to connect a brand new Mac mini (2012), with HDMI and Display port, to the cable network. I tried a number of different adaptors and combinations on both ports, but with no success. It didn’t recognize the tv output at all.

The newer Mac mini (2009) has a mini-DVi display port. So I bought a miniDVI video adapter and plugged it in. It didn’t connect to the tv network. It didn’t recognize the cable as a monitor in the way my old Mac mini does.

Now I am lost. I cannot add a display resolution in the System Preferences. I tried the option “Find displays” with no result. Why doesn’t it just work?