I had a similar problem with my Sony SXRD tv. I found out that I needed to go into the programming menu of the tv and actually attach a label to the relevant input. In other words, the inputs would only activate if they were labelled. That worked. Check your owner's manual and see if there is a tab in the main menu about labelling your inputs.
My wife has a Panasonic CT-27D11E Recently we tried to watch a DVD thru input 2 which is plugged into the rear of the unit. We were only able to receive the audio feed but no video came up on the screen. I unhooked the plugs and tried them in the video 3 inputs on the front panel of the tv, and got the same results. I then tried my PS2 in both inputs 2 and 3 but nothing changed. Less than a month ago I played the PS2 thru the front jacks without any problem. The part I dont understand is we can watch regular tv without any problems, so obviously the picture tube is still working. Any ideas?

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