A bit crytpic. Do I take iy you actually mean your cable box is feeding the Slingbox ? If so how ? And what about the HDMI question ? Please give us FULL details as to how you have the system wired up.
OK you confused me totally with the expression 'source TV'. I thought you meant that the actual TV, I now realise you meant the cable box. And I really don't see how you expected to see a picture if the cable box was turned off ?