Same here. All of the HDMI ports on my LD550 suddenly stopped working 3 days ago. All other inputs work fine. HDMI inputs display when a device is connected but when you try to use the device it returns a no signal message. Tried replacing the HDMI cables and performing a factory reset but to no avail. LG wants $200-$300 to repair. The TV is about 3 years old.
I have a LG LD790 TV connected to a DVD recorder via HDMI.
It was working fine (for over a year) but now displays no signal through the HDMI inputs.
I have tried different leads and have connected up another HDMI dvd player with different leads as well.
The inputs ARE displayed on screen (like it is recognising them) eg HDMI 1 HDMI 3 but when it tries to find the device it then displays no signal.
I have looked to see if simplelink was turned on or off by accident but it makes no difference either way (on or off).
I have tried a factory reset twice, so any suggestions please.
Is it a setting or a fault ?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic