The symptom sounds like a failed board. But it won't tell us which. Get repair estimates and STOP USING THAT TV. Continued use can blow out other boards and cause the repair cost to rise.
I have a Samsung 9000st and when i turn it on it cycles through the boot up and eventually comes on but it depends on how long it's been off for. If you turn it off you needto wait about half an hhour before turning on again and then there is no guarantee it will come on. Sometimes if you press the smart hub button three seconds after pressing the power button it does the trick. I have looked on the forums and have investigated the capacitor problem but havingremoved the back all the capacitors look fine. I have made several attempts to update the firmware but the TV powers down after the update and won't come back on so that has failed. I have just tried resetting the smart hub and doing a factory reset but this has resulted in the disappearance of the smart hub logo when you power up and i an currently sat hear listening to my TV turning itself on and off as it cycles through start up (without the logo).Does anyone have any ideas? If you require any other info let me know.