I have an LG LED TV model 42LE5300. The problem is there is an image when you do the flashlight test and there is sound. The only light there is are 3 small light on top of the screen.

You need to replace the LED backlight strips, you can get them from shopjimmy.com

Chances are it's bad backlights if you can see the image with a flashlight

This is a LED TV so there won't be an inverter board, they're only on LCD sets, what is wrong with your set is you have shorted LED lamps in the panel, its a common issue with this model TV, Ive replaced dozens of them in the last couple yrs, its not a fun job to do as the panel can be damaged very easily if extreme care isn't taken when handling it, watch some youtube vids to get an idea of how to do it...Good luck!!

Did you perform the Flashlight test ?
LCD LED TV Repair No Image Blank Black Screen Flashlight Test How to Fix...

Invariably a bad or defective back light inverter in LCD tv.
or LED driver board.

Perform a flash light test and follow the steps as shown in the LCD LED TV Repair No Image Blank Black Screen Flashlight Test How to Fix...

led light under screen is not glowing,,check led lights or its related circuit

Check the following link and watch the video from the other link provided in that answer. It has a guide to isolate the failure to a particular board.
have LG 47in tv sound but no picture and can see an image Replaced the...

Back - light problem. Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis.
http://electronicshelponline.blogspot.com/
Some model sets; especially LED back-lighted types; the back-light inverter circuit will be part of the main power supply board [SMPS]. In such cases, the power supply board might need replacement.

LG TV 3 blink code is due to bad power supply or LED lamps in the panel. If you have technical skills of soldering, physically check and replace if you found bulging capacitors in the power supply. If PSU is working, check LED back light strips with LED tester and replace faulty LED back light strip.