OK. This actually sounds most likely to be a main board fault, reasonably common with high end Samsung sets.
For this test you will be referring to the FAST TRACK guide I provided you. (Anyone reading this in future, PM me to get a free copy.)
You have a logic board and a main board in the TV chassis, among others. The main board is the one with all the HDMI etc inputs on it. Colour of main board may vary. They are sometimes green and sometimes blue. There is also a power board -- Samsung calls it an "SMPS board". This connects to the power cord. While the set is in operation, never touch anything on the power board to avoid electrocution.
There is a small orange ribbon going in between the main board and logic board. Very carefully unhook this cable from the main board end.
Unplug the connector going between the power board and main board, at the main board end.
There is a small, 2x2 pin header on the logic board. You need to take an alligator clip, or a jumper setting that would be used on a hard disk, or a paper clip, and jumper the pins numbered 3 and 4 together. Make sure this connection is firm.
Plug the power to the set in. The set should power on and a few test patterns may be displayed on the plasma screen. (If you see these, you know for certain the panel is OK.) It may then shut off, this is OK.
If it does NOT show any patterns: Unplug the set, plug in the connector between the main and power boards, turn on the set again. (You -may- only see brief patterns.) If so, see below.
If the above works (either of the above, with the main unplugged or plugged in) but the patterns don't persist: there is a label next to the connector on the power board which goes to the main board. Please get picture of it so I can see what connections need to be made. You will need some wire ties or hookup wire.
If it shows patterns and they persist: Replace main board.