It may be as something as simple as the power supply. I don't have any definititve suggestion except to get it inspected by a technician. While you're out of warranty, we do have technicians that may be affordable for this specific issue. As always, it's up to you to decide how to proceed, but if I can help out, please let me know.
Our (5 year old) Samsung tv turns itself off after a few hours and won't turn back on until it sits for a while. Then will run for shorter time period and turns itself off again. Unpredictable as to when will restart. Has been a great set--hopefully it's not ready for the recycler. Help appreciated. Thanks Eastsidejane