Powersurge made my HD setting revert to low def.
Your TV plays High Def material through either Input 4 (uses component cables R,G,B) or through Input 5 (Uses DVI cable).
Today most equipment uses HDMI cable for High Def or it may have a component (RGB) output that you can use. The DVI hookup is best, so you need a HDMI to DVI cable or Component Cables (Red, Green, Blue). You need some source that OUTPUTS High def (ex. 1080i) either through HDMI or component cable. You need to either connect the component cable(R,G,B) from the source to the Input 4 on the TV or connect the HDMI to DVI cable from the source to the Input 5.
You need to set the AV source on the TV to AV5 (if you are using the DVI input) or AV4 (if you are using component cables).
If you want to play Highdef source like Blue Ray then you can just connect the output of the blu ray player to your Tv using either the HDMI to DVI cable or component cable (Red, Green, Blue) and set the TV input to AV5 (for HDMI/DVI) or AV4 (for component).
But if you are trying to get Free High Def from an antenna then you will need to have a component that can OUTPUT high def. The $40 converter boxes don't do this - they simply convert the Digital signal to Analog (non high def). What you need is a High Def TUNER that OUTPUTS High Def. I was looking for one for this same reason and ordered the centronics ZAT 502 HD. But it cost about $80. Then I saw that Tivo had an upgrade deal where I could upgrade my existing Series 2 Tivo to Tivo HD for $99. It has a High Def Tuner in it. So I cancelled my order with Centronics and got the Tivo. In any case if you want Over the air HD you will need a High Def Tuner that will OUTPUT 1080.