@Failsafe
The normal reason for these messages is that you have not plugged a terrestrial aerial into the TV, as described in the paper Setup Guide(s) that you got with the TV.
If you have connected a terrestrial aerial, make sure the plug is pushed fully home, in the correct sockets, both on the TV and at the wall.
If this is already the case, then either (i) you have an indoor aerial, either incorrectly positioned or aligned or of insufficient sensitivity for your location (ii) you have a fault in your loft, roof, or shared, TV aerial system* or (iii) your TV is DOA (Dead On Arrival), and I would suggest you get it immediately replaced,
But if you don’t have a terrestrial aerial, you will need to obtain one to use YouView.
If you don’t want to obtain one, though, but to use satellite instead, either the built-in satellite or Sky, then you should disable YouView, as described in the FAQ at the top of this Community.
Then, for Sky, you can set the TV to default to the Sky input at switch-on, which is the most convenient way to use this TV with Sky as your primary viewing mode and the TV as its monitor.
If you are wishing to use the inbuilt satellite, though, be aware this is not Freesat, with a full EPG on a curated set of channels, more or less Freeview over satellite in effect, but rather whatever the satellite your dish is pointed at is transmitting, English or foreign language, free or by subscription, with only a Now & Next EPG.
* A common fault with distributed aerial systems is that they need a power supply, which has been inadvertently switched off or disconnected. You may need the help of a professional aerial installer with any or all of the items in (ii).
Please do let us know how you get on from here!
My favourite bedtime reading is a Sony product manual…
