LG 37LH40 won't power on

SOURCE: LG TV

There is probably a bad capacitor on the power board, I had the same thing happen to my 42LB1DR after 2 years. T.V. would turn on and white power light would blink, no pictue and no sound. If your'e a diy'er, it is not that hard of a fix. Take all the covers off of the back of the tv(UNPLUGGED!!!), then look at all the capacitors on the power board.
These are the capacitors, look to see if any of them appear to have a bump on the top of them. They are supposed to be flat, you can also tell if one of them has gone bad if there is an oily substance on the metal cover that was removed. If one of them is in question, carefully remove the board, and take it to an electronics store to have them sotter ?sp on a new capacitor. It ended up costing me around $40.00 to have this done. Good luck and if you are not comfortable trying this, than take it to a repair shop, but I was quoted around $450 to take the T.V. in. No Thanks

SOURCE: LG LCD flat screen TV - 42LG50-remote control is unresponsive

Sounds like a probable main board issue

SOURCE: LG 42PC3D-UE Turning on, clicking, then turning off & repeat

sorry i cant help, but i've got exactly the same problem on my LG, did you ever find a soloution thanks Pete

SOURCE: 42" LG 42LC7D LCD TV stuck in demo mode?

Did you have any luck? My LG is stuck in demo mode too. Menu button doesn't work, and keylock was on as default so I can't use the buttons on the TV itself.

SOURCE: LG Plasma 42pc3d turns on, pops, then turns off

The first thing you should look into is the Z-SUS board, the one situated on the right side viewed from the rear. This board develops a high voltage during operation that might be the source of the popping sound. It is also responsible in refreshing the panel for proper picture display. The weird colors on your TV indicates a faulty Z-SUS board.
Note: Unplug the TV and wait for at least five minutes in order to allow the voltages to drain before you disconnect or reconnect any connector.

• Disconnect the Z-SUS board from the Y-SUS board. The Z-SUS board is situated on the right side viewed from the rear of the TV while the Y-SUS is on the left.
• Plug the TV back and turn it on.
• You will still be able to see the weird colors the moment the TV shut off but do not flash. If it does not pop and stays on and there's a sound, you are pretty sure the Z-SUS board is faulty. Replace it.
• If it still pops and shuts off, disconnect the Y-SUS board from the power supply. The Y-SUS board also develops a high voltage during operation. The power supply is the one right between the Z and Y-SUS boards.
• Re-apply AC power then turn the TV on.
• You'll not be able to see any color or video. If it does not pop and stays on with sound, you have a faulty Y-SUS board, replace it.
• If it still pops and shuts off, please let me know.