Hello, I'm TV Tech1 and I'll be working with you to identify and help you resolve your problem.
So your TV may just turn on and then off, but other times it turns off, then restarts?
Part of the situation I try to identify is if the TV turns off BEFORE the LCD panel goes from pitch black to a subtle gray light level on the TV screen. Or does it light up a little, then goes out and shuts off.
Your TV has a power supply, and another board called an inverter to make the TV lamps light up. I usually try to see if the inverters are at least lighting up or not.