|If this happens on the TV when it's using it's tuner, it's defective.|
Those lines can only be caused by a hardware problem.
Return the TV to where you bought if they have a limited time return / exchange policy and it's within that, and get another one.
Or, get it repaired on warranty at a local place.
If this happens on the TV only when you have connected to it from the computer and have set the video input on the TV to the computer source, you could check the cable connection to make sure it's plugged all the way on both ends, try another cable or another way of connecting, but if that doesn't help, it's probably still a hardware problem on the TV, if you tried a different cable and that didn't help..