Hi I have a Samsung LN40A550 that once plugged in the red power light begins to blink and the bluish light in the middle is on but no picture appears. If you leave it plugged in it will eventually try to turn on but just continues to cycle. You can here the samsung tone once it tried to turn on and see the backlight for a second when you look at the back of the tv but nothing showing on the screen. I left it plugged in the other day for a little while and eventually it will turn on for a second show a complete screen of vertical green and other color lines and then shuts off. I have power to the TV and none of the capacitors a blown. Power supply is fine just wondering whether its the Main board that needs to be replaced or the backlight inverter. On time when it was on I here a loud screeching sound not sure if this help diagnose. Usually it just has a black screen with the red power light blinking as it cycles on and then off. Thanks please let me know what you think.