I'm sorry to hear that you're having this issue.
Based on your description, there's not much in the way of troubleshooting I can offer. I'd recommend having the unit serviced. There's no setting that will change it from powering down and turning back on.
Okay, I have a weird problem, and it seems to be getting worse: my Samsung LED 6300 55" TV just won't turn off... I'm having to unplug the bloody thing. Letting it set like this (has to be >hr), things go back to norm until the TV is heavily used again (basically the next night).