If all of your TV’s suddenly come up with the no signal message it usually means the transmitter is down. This happens more with the translators than the main transmitter at Mt Sugarloaf.
If all the sets say no signal, then there is no signal. The worst thing you can do is re-tune. You may tune in another transmitter and these pictures will be breaking up. (pixelating)
You will have no idea when your particular transmitter is back online, as you’ve re-tuned to the wrong one in relation to where your antenna is facing.
Also do not panic and bombard installers with phone calls. Check later in the day or that evening, and if it still not going by the next day, then you should ring your preferred installer.