Ok, you've tried to reset the software/firmware and did a hard reset to the TV's main board but none were successful.
You need to replace the main board to restore normal operation, so you'll have to remove the TV's rear cover screws, lift the cover off, and look at the main board's stickers and verify the BN number on it.
You can also check your main model number which has EXTRA letters at the end that verifies the model and part number of the main board matches.
Here is a website that sells the main board --
Copy and paste that into your web browser. You'll see a picture of the part, along with the full extended model number and the BN number they print on a sticker found on the main board.
I always prefer to look at the main board to verify the actual board installed on the TV set. That number is XXXXX most correct and concise number to order parts with.