Well, it looks like the issue is going to be related to the fact the Lamps aren't turning on, and that means the Picture and sound circuits won't start up since the lamps haven't passed the OK signal back to the TV's microprocessor.
So the micro could be dead, not turning on the lamps, or the lamps aren't lighting up and sending the OK signal back to the micro to advance to the Picture/sound enable level.
The fact that the TV won't turn on with the remote or the power button does seem to isolate it to the TV's main board. That is one reason why I'm going over that part of the symptoms with a "fine toothed comb" If the micro can't respond to you telling it to turn ON or OFF....and the lamps can't light....it really points to the micro/main board being faulty.
Would you agree with me that you cannot turn the TV on and off? On and off have the highest priority in the micro's command structure, and totally overrides any and all commands sent to it.
The only other command that overrides even the Power on/off command is if you started to download a firmware upgrade and it hasn't finished downloading.
So obviously, I would make sure that a firmware update wasn't being performed at any time previous to this issue appearing. Did your TV display any "updating" display just before it started acting up?
If not...then we have to replace the main board.