Lost picture. When using main power button, the

Your main board died.

There should be some fault with its main power supply regulator board circuit. Contact any service technician.

THe problem is in the set top box. Or common called the tuner box. IT looses the 5 volts to the main display and thus the monitor will go into a shut down state. THESE boxes are factory repair only and must be sent off to repair.

If you are sure that you have your TV on the correct input, you can try resetting the PS3's video settings using the following procedure:

1. Before changing cables, make sure the PlayStation 3 is turned off using the main power switch on the back of the PlayStation 3 (the 0 side is pressed down).
   
   
2. Unplug the power cord of the PlayStation 3 and television (or display) from the wall socket.
   
   
3. Make sure the HDMI cable is connected to the [HDMI OUT] port on the back of the PlayStation 3 system.
   
   
4. Connect the other end of the HDMI cable into the [HDMI Input] port of the TV or display monitor.
   
   
5. Plug the PlayStation 3 and television (or display) back in to the wall socket.
   
   
6. Turn the main power switch on the back of the PlayStation 3 back on (the line on the power button is now pressed).
   
   
7. While the PlayStation 3 system is in standby mode (red light on the front of the system), hold down the touch-sensitive On/Off button on the front of the system until the system goes into standby mode again . (So the light cycle would go from: red light to --> green light --> then back to red light) This will ensure that you have held down the On/Off button long enough to reset the Video Output Settings.
   
   
8. Turn ON the PlayStation 3 and once the system finishes powering up, the Video Output Settings will automatically reset to the standard resolution (or detect the current display output settings of your TV/monitor).
   

If that does not resolve your issue, try the other steps here:
http://us.playstation.com/support/answer/index.htm?a_id=262

Did you try this yet

SYSTEM RESET
If the TV will not respond to either the remote control
or the front panel controls and/or will not power Off,
press the SYSTEM RESET button with a pointed item
like the end point of a paperclip. The TV will turn Off
and the TIMER light will flash quickly for about one
minute. When the TIMER light stops flashing, you may
turn on the TV again. Changes you made the last time
the TV was On before you used the SYSTEM RESET
button may be lost, however, the changes you made
previously are not lost.
POWER/TIMER Indicator
The green light is a multi-function indicator. This light
will flash rapidly for about one minute each time the TV
is plugged into the wall electrical outlet, when power
is restored after a power failure, or using the SYSTEM
RESET button. Do not attempt to turn on the TV again
during this period. Wait for the flashing to stop and
the light to turn off, before attempting to turn the TV
on. While the TV is powered on, the light illuminates
steadily. If the TV has been programmed to turn on
automatically using the Timer feature,

power inverter board is dead.
need a new one.

power button broke need replacement

Resetting the TV
If the buttons on the remote AND the buttons on the TV case do not work (channels do not change and you cannot open or navigate the menu), the TV has stopped responding. Reset the TV as follows:

NOTE:
Some TVs have a reset button. If available and accessible, try using the reset buttons before using the steps below. Using the reset buttons can save time.
1. Unplug the TV power cord from the power outlet.
2. Unplug any connected devices (DVD, Set-top boxes, etc...)
3. Press and hold the TV power button for five seconds.
4. Plug the TV power cord back into the power outlet and turn on the TV.
5. Open the on-screen menu to confirm that the TV is responding again.
6. Turn off the TV and reconnect the devices.
7. Turn on the TV.



LCD TV TroubleshootingThe defective LCD TV may have the following common symptoms:

Symptom: No picture on screen but LCD TV still has sound.
Solutions: The problem is cause by defective inverter. Replacing ivnerter will solve hte problem. Symptom: Screen flash on and off between 1/2 to a few seconds, but power indicate light stays on and TV still has sound.
Solutions: The problem is cause by defective inverter. Symptom: Blue Screen but no picture
Solutions: The problem is cause by defective Main Board(AD Board). In some cases, this problem may cause by the defective Screen Controller board. Thsi board is mounting on teh back of LCD TV Scree. Symptom: Power light stays on but no display and sound
Solutions: The problem is cause by defective Main Board(AD Board) or Power supply board. Symptom: No Power or Power indicate light does not lits
Solutions: The problem could cause either by defective Power supply board or defective Main Board(AD Board). Symptom: Screen is half dim and half bright
Solutions: The problem is cause by defective LCD Panel.It needs to be replace.


Hope it may help you;

Regards;
VOTIT

Hold down the "input" button and "volume -" button while the MAIN POWER BUTTON IS OFF. Then turn on the main power button while those are held down, the light on the tv & avc box will turn green. When it turns green, immediately let off the 2 buttons and press "volume +" button, then press the "Main Power" button. Next step is to repeat the process about 20-40 times & the TV WILL WORK!. I have read that this may have something to do with the energy star compliant commands that can changed through the serial port.
The above is from psxpirate25. Thanks!
I had to repeat the whole process a couple of times to get rid of the factory setup firmware mode. Do it 40 times, I would mess up the sequence a couple of times. Keep trying, it does work.

What is your model number