Most often, this symptom is a result of a failing POWER SUPPLY but a faulty MAIN BOARD can certainly cause very similar symptoms. Unfortunately, without a donor TV to swap parts with or a dedicated test rig, it can be very difficult to differentiate between these problems.
One quick way to test this is to remove the rear access panel on the TV and replace the power supply circuit board with a new one, since this is the most often the source of the trouble.
You can usually find replacement supply circuit boards online by searching for your TV's model number.
Here is a link to a replacement POWER SUPPLY IRCUIT BOARD for your TV currently available on Ebay for about $39 US plus shipping:
And here is a link to a replacement MAIN CIRCUIT BOARD for your TV in case you needed it currently available on Ebay for about $59 US:
Just use your mouse to click on the links, which are the underlined and highlighted text just above. This will open a new web browser page automatically for you and allow you to view the information and items at the website indicated.
The repair / replacement procedure is not extremely difficult if you have some basic electrical safety knowledge and some basic electronics / mechanical repair skills.
You will need to unplug the power cord from the unit, lay the TV screen side down on something soft and flat like a bed if necessary, and then remove the rear access panel or the entire rear cover as required in order to access the circuit boards inside.
When you remove the rear cover and access the circuit boards inside, just check the part number that is printed right on your circuit boards and confirm that they exactly match the ones provided in the Ebay listings. Also make sure that any part you order is labelled "TESTED WORKING" in the condition description. Any part with a condition description of "AS IS" is probably faulty itself as well.
Then unclip and remove the various electrical wire connectors leading to the power supply circuit boards. Then remove the screws securing the circuit board to the TV frame and then remove the power supply circuit board. Be sure to avoid touching any large capacitors on the circuit board which can retain a nasty charge even after the unit is unplugged.
Then just screw in the new circuit board and connect all the wire bundles to their appropriate connectors on the new circuit board and then replace the rear cover. Then plug in the power cord and test.
Here is a link to another Expert's solution to a similar problem which includes links to his excellent and informative set of LCD TV / MONITOR TROUBLESHOOTING GUIDES:http://www.fixya.com/support/t10008425-when_turn_tv_picture_flicks_off
These guides will give you some idea of the various problems with LCD TVs and monitors and the associated repair procedures.
If you choose to rate BUDMRTN's troubleshooting tips by clicking on the YES THIS WAS HELPFUL icon on his solution page at the above link, then I thank you very much for your time and consideration.
Please comment back here to this page if you have any details to add, have any questions, have difficulty with the links, or just require further general assistance and I will respond as soon as I see it.
I hope that was helpful to you, good luck.