If the above method does not work, the LNB may have a fault.
Press the [SERVICES] button and then press    then [SELECT]
On Sky HD, press the [SERVICES] button and then press    then [SELECT]
Press the buttons in the sequence above exactly - do not atttempt to use [UP] or [DOWN]. Note that when you press the second 0 and 1 nothing happens on the screen until you press the final [SELECT]. This is a "hidden menu".
Your first action should be to switch off the Sky box with the remote control and then unplug the mains supply to the box by switching off the mains socket and pulling out the black mains plug from the back of the Sky box. Then wait at least 5 minutes. Then put the mains plug back into the back of the Sky box followed by reconnecting the mains supply and switching that on. Then wait another 5 minutes to let the Sky box set itself up again. Then use the remote control to switch it back on to its normal operation and check that the TV shows a picture and gives sound (it will normally show channel 998 first). If all is well then problem solved. If you still don't get sound and pictures, try changing channel to 101 and you should get BBC1. If not, then the Sky box probably has a fault that should be reported. If you took out the insurance it should be covered, otherwise they will charge.
I have 2 Dion DigitalSet Top Boxes that I've had for some years. All of a sudden one of them has lost all the channels. I have tried retuning, factory reset, everything, but it just keeps saying 'no carriers detected'. I haven't moved anything around and have checked that nothing has become dislodged. The other box is still working fine.