Samsung ln-t4042h turns on, plenty of sound, backlight works,...

This model has a history of bad electrolytic capacitors on the power supply board. I would definately start by looking at all of them. If any of them are bulged or domed on top rather than flat, then you should replace them. Just make sure you put them back in w/ the positive and negative sides in the correct position. Good luck!

Take ur tv aparts.The power supply board is the board that ur power A/C power cord go into it.U know basic electronic.U have soldering iron,know soldering,and solders?Check all around the power supply board.Look all around the power supply board,check and see find any defective gases leakage capacitors.These dead capacitors alway have bulges or fuff up it top.Replaced these dead gases lekage capacitors will solved ur power problems.Or tries Websites like Shopjimmy.com,Ebay.com to buy a whole refurbish power supply board for the replacement.

bad capacitors on power supply

U have sound,after picture fated?Ur LCD inverter board it dead.must replaced this board to get the picture back.It usally a long board.Tries Shopjimmy.com,Ebay.com for the board part.

the plasma is leeking in it call a repair shope for TV's dont doo it your self

It can be one of the two parts, LCD controller or the LCD panel itself.
http://www.shopjimmy.com/catalogsearch/result/?q=Samsung+LN-T4042H+

Picture of the screen shot will help.

Look for screen setup for AUTO ASPECT in the setup menu, turn it OFF.

There is a problem with the power supply in your TV. The regulator switch is causing teh clicking sound you hear. In order to fix it, you will need to replace the power supply. This is done by taking off the back cover of the TV, locating the power supply which is usually a yellow board that will have many high voltage capicators on it and replacing it with a new one.

i fixed it, on the PS3 u hold the power Button while holding then Switch the power button on on the back for like 10 sec and it resets the picture settings to default

Verify that the INVERTER is working correctly and outputing the correct voltages.
If that is the case you should look at the CCFT (Cold Cathode Fluorescent Lamp) what are pencil thin fluorescent lights around the LCD panel. They claim these will last 50 - 60 K hours but they are still lights.