I'm very sorry for any inconvenience this may have caused you. Unfortunately, this sounds like it may need servicing. Here's the thread where you can get details on setting that up: http://forums.cnet.com/7723-13973_102-542437/service-issues-click-here-for-help/
We got our TV (Model # UN40F6400AF) about a month ago. It worked wonderfully until this past Sunday (superbowl!!) when it started to shut down on its own. Since then it has become pretty much impossible to watch the TV. It shuts down on its own - then turns on and then off and then on and then off. Sometimes the red light on the front blinks - sometimes it doesn't.
How do we fix this? We LOVED the TV until this.