Assuming the problem is present in all input modes (DVD, Cable, VGA etc) then, depending on exactly what type of Flatscreen TV you have (LCD or Plasma), the problem is usually in either the power supply circuit board or the LCD Controller board (TCon board).

Bad capacitors in the power supply can cause a low quality voltage supply to the other components in the set which can manifest in any number of ways. If you see any burnt or bulging capacitors on the power supply board then that is almost certainly the cause of your problems.

You can buy a complete replacement power supply circuit board for most TVs on EBay for about $50 or so, and just open up your set and replace it yourself. If you are the least bit handy with a screwdriver, it is not an overly difficult task.

As I said, it may also be a bad LCD Contoller Board (TCon Board) but, since you did not provide any details about the exact type and model of your set, I cannot really provide any more significant detail than this for now.

Here are some links to another (BUDMRTN) expert's excellent LCD Troubleshooting Guides that you can read through and get an idea of the LCD repair process:


http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide

http://www.fixya.com/support/r6150077-basic_lcd_monitors_troubleshooting

http://www.fixya.com/support/r7406380-tv_training_manuals

http://s807.photobucket.com/albums/yy352/budm

http://en.wikipedia.org/wiki/Capacitor_plague

Please leave a Thumbs Up rating on his pages if you find his guides helpful.

Please comment back here to this page if you have any details to add, have any questions, have difficulty accessing the links, or just require further general assistance and I will respond as soon as I see it.

Thank you very much and good luck.

Joe.