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/
Samsung LN46B650 randomly shutting off and restarting. This problem is currently intermittent, only several times per year after first 18 months. Is this a common problem?