Thanks for reading. I have phoned Swann and, with their help etc, all is now working well. The reason it wasn't working was because, when selecting input, I tried all of the options except 'PC', thinking that option wasn't what I wanted. In fact, on selecting 'PC' (with VGA connection) all worked perfectly !!!
Anyway, I'm so pleased it's all sorted now. :) Unfortunately, there's no tick to indicate 'Solved'