Tried connecting our portable DVD player to our Samsung TV last night using an AV lead I had lying around (jack style plug one end, red, white, yellow connectors the other).

But I couldn't get any picture or sound. TV knew something was connected as gave me the option to select the AV source.

I also tried the scart connector which has the coloured connections that came with our Wii, but again nothing.

Does anyone have any ideas how to get this working or what is wrong?

I know the jack socket on the DVD player works as I can pair it to another (master/slave) to take the feed and display it from using jack to jack lead

It could be sensing the voltages from the cable but not signal ones that it can decode. I have never used such an adapter so not sure if they are considered standard or can vary in configurations.