LG 55LV5500 turns on but no picture or sound - LG 55LV5500 55 Class 1080P 120Hz LED TV with SmartTV, Smart TV, LED Backlighting, TruMotion 120Hz, Wi-Fi Ready, FuHD 1080p Resolution, DLNA Certified, ENERGY STAR Qualified, Picture Wizard II, Intelligent Sensor 55LV5500 55-LV5500 555500 55-5500 55 LV55

It could be either the main or power board, if you are comfortable doing it pull the back off and look for a pin on one of the connectors that says PSON...stands for power switch on and measure the voltage at that pin, if you have nothing the power supply board is bad, if you see a few volts on that pin push the power button on the TV and see if the voltage changes, say if its at 3 volts does it go to 5 volts or if its as 5 volts does it drop to a couple volts, if you see that happen then the main board is working and you need a power board, if there is no change its the main that is bad...Good luck!

If you wish to get some details; check the site linked here. Pull up older posts. Surf the site with patience.
http://electronicshelponline.blogspot.com/
Faults & possible causes to LCD screen are given with illustrations. You can get an idea about the fault to an extent. Faults to all LCD screen are similar, irrespective of its brand and screen size.

Fault at its main digital board. Short circuited component/s at it. Contact any service technician; or the authorized service center. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts.
http://electro-medical.blogspot.com/
http://electronicshelponline.blogspot.com/
In most cases, the main board might have to be replaced. If so, a software [firmware] update too might be necessary.

Better antenna.

I think a surrond sound system helps. I have the same problem, i can't hear dialogue either. I can't afford surround sound system so i have to keep turning volume up & down accordingly.

For your best hearing pleasure you should try using your optical line using a fiber optic line. 55lv5500 has optical out so check if your home theater has optical in also

According to the LG websit, to factory reset your LG 55LV5500:

Press the HOME button to access the Home Menu. Press the arrow buttons to scroll to SETUP and press ENTER. Scroll to OPTION and press ENTER. Finally, scroll to INITIAL SETTING and press ENTER. This resets the TV to the factory default settings and erases all stored channels.

Try a factory rest (settings, options, factory reset) and if this doesn't help contact LG for a repair.

The main digital processor board should be suspected. Contact any experienced service technician.