When I power on the TV both picture and sound comes on. About 2 seconds later the sound stays on but the picture goes off including the backlight. I have tried to do a factory reset as suggested in posts but that did not work either.
First check it by connecting a DVD player or games console to it to see if the picture behaves with them feeding it. I will assume they also fail. When it fails try going up a channel and see what happens then. So If the backlight (which is a few simple flourescent tubes) also went off AND the sound went off I would say there is a fault in the power supply, inside the TV, but the sound stayed on so this is a very unusual fault. I think it may be switching to a mode of operation where the picture is deliberately suppressed. A factory reset should have cleared this so there is an electronic problem, for most TVs its not cost cost effective to repair any of the internals.
SOURCE: sony bravia kdl-52w3000, turn tv on, no picture or
Most likely this is caused by a defective main board. Changing the main board will fix the issue about 95% of the time.
To be absolutely sure, the voltages need to be checked on the power supply. If they are not the values listed in the service manual, then you should replace the power supply instead (accounts for the other 5% of the time).
SOURCE: Sony Bravia KDL-V40XBR1, no picture
You either have failed 24vdc power supply section or failed backlight inverter board, check for 24vdc first, look for caps with leaking/bulging top.
Parts: http://www.shopjimmy.com/catalogsearch/result/?q=Sony+BRAVIA+KDL+-V40XBR1+
http://s807.photobucket.com/home/budm/allalbums
http://en.wikipedia.org/wiki/Capacitor_plague
http://www.badcaps.net
SOURCE: tv turns on has sound
Have flashes of picture about 30 sec, or so?Than the 2 long LCD inverter boards are dead,have backlight make no difference.Tries to reset the tv back to factory setting by,unplug,replug the tv and cable box back about an hour later,let the tv Tuner board to reset it self,the cable box upgrade it softwares.After this,u still have the same problems,than the Tuner board is dead.Tries websites like Shopjimmy.com,Ebay.com to buy the 2 long refurbishes LCD inverter boards or the Tuner board for the replacement.
SOURCE: tv doesn't turn on ....i
Plasma and LCD TV sets are prone to having capacitors in the power supply section fail. This is the most likely cause for the probem you describe. When capacitors fail your will commonly see one or more of the following symptoms.
Again, You can get a power supply repair kit with the parts, detailed instructions, and support from sites such as www.TvRepairKits.com . Or just click here to see more details on their kit.
Here are pictures of capacitors...Notice that the ones below look bloated. They have failed and will need to be repalced. 
Capacitor being replaced! Fairly easy DIY fix. 
Again, You can get a power supply repair kit with the parts, detailed instructions, and support from sites such as www.TvRepairKits.com . Or just click here to see more details on their kit
SOURCE: SONY BRAVIA KDL-40s4100 is not working right
This is a common problem with these sets and NOT an easy one to fix.
You may have a bad CFL lamp which is located under the LCD screen.I have fixed quite a few of these,its not easy fix but not impossibe.
Ed the tech
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