Samsung LCD TV Turns on ok for about an hour, than the screen turns black with Audio?!@?

Model# LA40A550 mfg date 2008, The TV works OK when it works. after the screen tuns black it will not turn on by itself. i need to turn it off wait for a while and than again it turns on ok but not for long. I have looked at it while dark with a flashlight and can see a faint video picture. I have opened the... show more Model# LA40A550 mfg date 2008, The TV works OK when it works. after the screen tuns black it will not turn on by itself. i need to turn it off wait for a while and than again it turns on ok but not for long.
I have looked at it while dark with a flashlight and can see a faint video picture.
I have opened the back a looked at the Caps , they look OK, not swallwon or anything strange, i also checked the connectors and they are all in place. I need some advice what to do next, which and how board to test , as i am trying to fix it by myself due to shortage of funds, cheers.
Thanks for all
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