Sony WEGA KV-34HS420

I have Sony WEGA KV-34HS420 TV. I currently have a HD cable box that is connected to the TV. The box is connected to the TV's Video Input 5 via video Y,PB,PR and audio (L/R) jacks/cables. The TV has been working fine for about a year. Recently I turned on the TV and I tried to watch HD TV via Video Input 5 (HD input) and the color looked terrible (ie no red and very dull lacking any bright colors). I went to the video settings and the color could not be changed or enhanced. When I changed to Video Input 1 (basic cable TV input...no HD), the color was fine. I thought there may be a problem with the HD box so I connected another HD box to the TV. I had the same color problem on Video Input 5 with this box also. Does anyone know what the problem may be? Could there be a malfunctioning component used in the high definition circuitry that is causing a problem? If yes, what component could it be and how easy is it to fix? I am dreading bringing the TV to a repair shop because it is very heavy and difficult to move. Any help would be appreciated. Thanks, Jeff