Check to make sure that your television's input is named "PC" rather than "----". You also might check to make sure that your video drivers in the computer are up to date, and that your secondary monitor's settings are set correctly. It may be mirroring the settings on the laptop screen.
I am using the PC input to use my Samsung UN46B6000 as a monitor for my Compaq nx9420 laptop. I am running Windows XP. I tried the auto adjustment on the TV and reduced the laptop resolution from 1920x1080 to 1024x768. It is running at 60 hz. The TV is showing approximately 60% of what could be viewed on the laptop screen. The horizontal bars flicker as well. Please help.