First, let's determine whether the problem is in the TV, or coming the source. Grab the TV remote control and select 'Menu'. If the menu hides the abnormal lines or bars, then the problem is likely the source rather than the TV. But if the artifacts are visible even over the menu, then the problem is in the TV.
To further diagnose the problem, change how the picture fills the screen. Find the button on the TV remote labeled "WIDE", "ASPECT", "P SIZE", or "ZOOM", and push it to change the mode. Do this several times and see if the lines or bars change position with the picture. If the abnormal lines or bars remain stationary in every mode, then the problem is in the TV. Ninety percent of the time, the problem can be fixed by replacing the display panel. Otherwise, replacing the main signal board will solve the problem.
If you are not sure whether you should fix the TV or buy a new one, read Is My TV Worth Fixing?
One or more thin (pin stripe), solid, vertical lines of any color - or many thin, solid, vertical lines of random colors
These symptoms mean there is something is wrong with either the display panel, one of the address printed circuit boards, or an electrical connection between them. The best way to fix it is to eliminate all of the possibilities by replacing the whole panel. The new panel will come as an assembly with all of the printed circuit boards it needs, all hooked up and ready to go. (For plasma TVs see How to Replace a Plasma Display Panel. For LCD or LED TVs see How To Replace an LCD and LED Panel.)
A combination of randomly colored, solid, horizontal and vertical lines and solid or semitransparent, randomly colored bars of a non-symmetrical pattern
This symptom always means there’s something is wrong with the panel. The best way to fix it is to replace the whole panel. (For plasma TVs see Replacing Plasma Display Panels. For LCD or LED TVs see How To Replace LCD and LED Panels.)
Exactly half of the picture (left or right) is perfectly okay and the entire other half is not
If you have an LCD TV, the culprit is a defective timing controller (TCON) printed circuit board. This is the board that feeds the picture information to the LCD panel, and centrally mounted near the top or the bottom of the panel.
If you have a plasma TV, the guilty party is the address printed circuit board on that side of the screen. The address boards are mounted either along the top or bottom edge of the plasma panel. See Replacing Circuit Boards
One or more black vertical bars, each from 1 to 3 inches (2.5 to 7.5 cm) wide
This is not the same as “pillarboxing” (the two black bars that you typically see on the left and right side of a narrow 4-by-3 video source). See TV Picture Doesn't Fit Screen for more infomation on this.
If it is an LCD or LED TV, the only way to fix it is to replace the LCD/LED panel. See Replacing LCD and LED Panels.
If it is a plasma TV, it could be a bad address printed circuit board. The address boards are mounted either along the bottom edge of the plasma panel (which is most likely), or along both the top and bottom edges. Or the problem could be that there is something wrong in the panel. To eliminate the ambiguity, the most reliable way to fix the problem is to replace the whole panel, because the address boards always come with the replacement panel (along with other printed circuit boards). See Replacing Plasma Display Panels