we checked if it was grounded/wired correctly with one of the testers that you plug into an outlet and it read as being correct.

The TV that sparked and caught fire is not new. The new TV that we bought we hooked up to our box downstairs (we've had that box for over a year). The TV that sparked and caught fire was hooked up to that same box mintues before we hooked it up to the new box and that's why I don't think there was anything wrong with the TV. It was about 16-18 months old, so it was out of warranty.

Maybe it was a fluke. But my perspective is that the voltage is correct, the wiring is correct, the TV was in working condition hooked up to a different box minutes before.
So to me, it seems that either something went wrong w/ that cord when the first box blew up or there was something going on with that box.

I don't know... maybe it's unsolvable!