No video output from Xbox 360

I have had my xbox 360 for a long time. I have tried all the basic troubleshooting relating to similar matters.

I have: Changed the power block. Changed the HDMI cord. Bought new AV jacks. Checked correct INPUT on tv. Made sure proper INPUT CHANNEL.

Now here comes my dilemma.

My 360 boots up fine. Registers controller. Registers hard drive connection (it was once a problem, but it has been resolved). I get no sound nor visual output. I know my console has fully booted up because I know the exact button commands from boot up, to start the one game I play on this console (Skyrim), the console recognizes the game and you can distinctly hear the console get to work as it loads the game. I have even started a new game, I get the controller vibrations from the opening intro to game play, still no sound or visual output.

Any ideas before I send it off to fix or to its grave?