Hello, I'm TV Tech1 and I'll be working with you to identify and help you resolve your problem.
There's two issues I see here.
1] Turns on and off by itself -- If the TV is turning ON or Off, your model may have what we call CEC (Consumer Electronic Control) that let's things like amps and DVD players turn on the TV when the power button is pushed on their remote control. The key is that your TV doesn't do BOTH within 30 seconds. Both would be a failure within the TV set if no other buttons were pushed on the remote.
Also, if there is NO Signal being recieved by the TV set, the TV will turn itself off after 10-15 minutes. Saves on energy.
2] Won't let you store demo mode -- If the Demo mode is running all the time while you are attempting to watch TV, then we want to set it to HOME MODE so the Store Demo mode stops trying to sell you on the features of your TV set.
Does any of your symptoms match this ??
wont let you go to home mode
To do that, you have to set your TV's input to the TV tuner.
Then the Plug and Play setting in your menu will light up and give you access to it. Then select Plug and Play, and in there you get to select Store or Home mode, then you have to complete all the settings, including Autoscan for the tuner, even if you don't use the tuner. Once it finishes, it will store and keep those settings. If you only do a part of the Plug and Play settings, it won't store them, and it will revert back to the older settings.
switchs on and off by its self
How long does your TV stay turned on? Is it less than 30 seconds, or is it shutting off after 10-15 minutes all the time? Does it do this whenever it feels like doing it to you?
can be any time grandaugther watching cebbies when it started
Ok, that does sound like your TV may be sensing a No Signal condition even when you do have a signal. A lot of newer TV sets actually sense if the TV is actually getting a signal, some expect you to push buttons on your remote so the TV knows if you are actually watching TV, and others sense people moving around the room, indicating that people in the room are not sleeping in front of the TV set....
Those are all energy saver settings on the newer energy saver TV sets. I think they've been around since at least 2009, and I've had customers complain about their TVs doing that to them.
Here is how you check that --
Press your menu button, arrow down to the SETUP menu, then right arrow into it. Now arrow down to your ENERGY SAVING setting, arrow right into it then select OFF. If it is off, it won't turn off if your unit monitors the activity of the remote control or a proximity sensor that monitors that you are moving around in the room. It may also deactivate the No Signal shutdown.
That may stop the TV from at least turning itself off.
Right now, I'm just throwing out the "possibilities" that I've seen on TVs. We'll try to take this a step at a time, but I would also suggest you check your Plug and Play mode -- That is also listed in the SETUP menu settings. I suggest STARTING with the Plug & Play settings when the TV's input is set to TV, not Video 1 or HDMI 1 etc....
You do the Plug and Play first, simply because the ENERGY saver settings may get set back to a Low/Medium/High setting. That's why you do that AFTER Plug and Play so it remembers you setting it to OFF.