My sony kdl-42v4100 its turning off every 10 to 15 secns and the tv is going to standby mode.. how i can

The TV enters standby mode when there is no signal for 30 seconds. https://docs.sony.com/release/KDL46V3000.pdf
I searched standby using Ctrl+F and found this information. It seems you should be able to bring it out of standby using the power button on the remote. You want to make sure there is an input connected and if it is connected to a PC that the PC isn't telling the TV to go into standby.
Try pressing the input button and changing inputs once you press the power button and the Standby is flashing.
If this doesn't work you may need to contact Sony Support.
1-800-222-SONY(7669)

Check all fuses. If you have power going into the power supply board..but none coming out of it...I think you have found your problem. Get a new power supply board.

I have encountered this before---there are set top boxes that will convert the NTSC to PAL and the only other concern is the line voltage being the same or not.

capacitors on your power supply are bad. I normally remove it and replace, or send the old one totvpartsandmanuals.com and get a discount on a new one. You can get it c.o.d. or have the same one refurbished

This is called "clouding". It is very common with a lot of the lcd panels. I suugest going to sonys e support website to see if it might still be under warranty. I have a sony lcd tv that I purchased back in 07 and its under warranty until october 2012. If it is still under warranty then sony will fix it for free.

Hi there

this is not meant as a solution, but a tip if you`d like to get an answer.
You should clarify in which occasion you get either sound and no video or black screen with sound.
This is a little confusing for a repairman.

Hi,

Sounds like there is a short on the power board or the power board has gone faulty.

Look on the power board to see if any of the capacitors are bulged or if there are any other components burnt out. The TV is going into protect mode because of an over current, which points to a short on the board or a component has gone short circuit.
Thanks

If the Standby light is blinking at the front panel of the TV, it seems that there is an internal malfunction occurred in the TV.
I will forward a link to a page where you can get more information and troubleshooting steps for this issue.

http://www.kb.sony.com/selfservice/microsites/search.do?cmd=displayKC&docType=kc&externalId=C399467

Please perform the steps provided on the page. If the issue still persists then service of the TV is required.

sony 52 inch tv in stand by mode comes on and off on its own

it is your HD box. get another one.