We have an LG 42lb1dr 42" HDTV LCD TV and all of a

It is most probably the power supply board. There is a repair service for this board available at http://www.coppelltvrepair.com/p/791/lg-42lb1dr-ua-power-supply-board-repair-serivce-for-totally-dead-not-powering-on-or-shutting-down-tv

Have you tried changing the batteries?

I have the same TV. Just take a deep breath and listen. My TV stopped so I did much research and came to the conclusion that there are 5 capacitors that were causing the problem. I did it myself for $15.00. I don't want to tell you how to do it because of liability. Do a lot of research on the internet and also LG will send you schematics on the internet. I am currently having a problem of my TV coming on at random times, so I am now in the process of figuring that one out. Don't be discouraged. I like my TV. Sometimes these things can be frustrating but remember when it was so much simpler. No need to cuss and get angry. God bless you and good researching.

check the menu for power saving option if it`s on shut it off.

replaced main board

There are 4 capacitors on the power supply board that need to be replace. They are in the same area, same color, look for bulged caps.

This is probably bad capacitors on the power supply board. My LG 42LB1DR has a known problem with this and I replaced the four bac capacitors myself and saved 5-6 hundered dollars that I was also told that it would cost to fix. I fixed for under 10 dollars and about 20 minutes. LG knows about it but they dont really want to admit it. My TV was only 26 months old when this happened. The four capacitors are made by Samxon and are 2200uf @ 10v. They are junk so even if you have the entire board replaced for say $200 its just going to happen again. They need to be replaced with a different brand.

Probably power module bad.

This could be bad capacitors on the power supply board. My LG 42LB1DR has a known problem with this and I replaced the four bac capacitors myself and saved 5-6 hundered dollars that I was also told that it would cost to fix. I fixed for under 10 dollars and about 20 minutes. LG knows about it but they dont really want to admit it. My TV was only 26 months old when this happened. The four capacitors are made by Samxon and are 2200uf @ 10v. They are junk so even if you have the entire board replaced for say $200 its just going to happen again. They need to be replaced with a different brand.

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