Is it still intermittent? Will it ever come on, as you indicated before in this thread? It might be that the physical connection for the display is loose on the mainboard. Rare, but it can happen.

Also, do you notice a multisecond pause between applying power and the standly LED pulsing? That multisecond pause would be caused by the player going into the boot cycle - the standby LED is not on during that period. If so, that might indicate that the player is booting.

Lastly, please triple check (I know...) your serial configurations. The type of error / failure that I know would cause no output on the serial port is so catastrophic that you would not be seeing any good LEDs at that point.