Depending on how old the set is, find out your statutory consumer's right. Beside the guarantee you are also covered by govt. legislation that you can expect trouble free enjoyment for a reasonable time from a new appliance.
Everything can be repaired but if the set is over 3 or 4 years old it will probably be better/cheaper to replace it.
I had a TV that did the same thing. It started switching itself off once or twice a day, then more frequently until it only stayed on for a few seconds. The problem was the standby control which normally operates only when you switch onto standby. I had to buy a new TV and I'm pleased I did as I hadn't realised how poor the old picture was.
You can get yours repaired if it's worth it suna. I think it's probably a new TV though.