Hi there and welcome Peter
If the TV switches off then it does not point to a signal problem, as it would not force the TV off.
First, can you do the following please
Can you please remove the power to the TV (so unplug it from the power socket).
Then on the actual TV, hold the power button for 60 seconds then release.
Then wait 10 minutes, connect the power again to the TV, turn it on and tell me please if it is now operating correctly.
Let me know the results please