I have a VPW450HD set that I just fixed. I get the feeling that they are not all the same inside, but this may be the same problem many of you are having. When turned on the green light on the front of the set would come on, if in a dark room I could see that there was some light to the screen ( not much ) but no picture and no sound. When I pushed the power button to turn the set off - it would not turn off. I had to turn it off from the main power switch on the back.
If you take the back off you will see a large square board in the center of the TV ( about 12" X 10" ). I would describe this as the main power supply board. Near the top there is a two wire connector with a Red & Black wire in it. Follow this wire up to the next board. It is a smaller board ( about 5" X 3" ) with the Red & Black wire connector near the top right corner. I would describe this board as a secondary power supply board. It sends the power down to the input board. On the secondary power supply board there is a six connector plug on the left side of the board. This is where I found the problem with mine. The connector is burnt and melted because of a " cold solder " joint. Carefully remove the secondary power supply board - you may be able to use the same connector if it is not to burnt and brittle. The six pins on the solder side of the board need to be re-soldered. These pins are thicker material than the other solders, and so do not solder well in a wave solder process. the pins do not get hot enough to solder properly, so over time an opening is created between the pin and the board.
Make sure you do not change the order of the wires if you have to replace the connector or if you solder the wires directly to the board. If you use the same pins and connector - check that they will make good contact. Often there is a residue on the pins and the small clips in the connector. I took the wires out of the connector and cleaned them ( one at a time ) with a small wire brush. A razor blade also cleans them well.
I hope this helps some or all of you !
Let me know if it worked for you or if you have questions.