My 550 is not starting . It gives a click sound when it starts like in normal operation, the panel brights up and within 1 sec the set automatically shuts down, This happens for 3 times (starts and stops). If you press the start button again the same thing happens. Called the LG service guy, he says need to replace the power unit. Shall post more on what happens when he replaces the power unit. Set is out of warranty. So don't know what will be the bill like.