This sounds like a common occurence I have to fix for a lot of customers' boxes at work. Sounds like your Sky box has locked up to me. Do this:
Hold down the "Backup" button on the front of your box, and while still holding it down pull the figure 8 mains lead out of the back of the box. Leave it out for 20-30 seconds, then plug it back in, but
keep holding the "Backup" button.
After 10-30 seconds, all the lights on the front of your box should light up. You can let go of the button now. If your box is wired with a SCART lead to your TV, it should automatically pop up on screen and tell you that it is doing a system update which should take about 10 minutes. If you don't have a SCART lead in place, just change to the channel you normally watch Sky on (e.g. 6) and you should see the message.
In my experience, it could take anywhere between 2 and 20 minutes. When it has finished the lights on your box will go out. Wait a few minutes and then turn your box back on. I say wait a few minutes because the box will be unresponsive for that time while it sorts itself out.
Once its back up and running, if a new software update was available, you will have that update. There was a recent update which has a few graphical changes, most notably to the Sky Guide, so you may see a few differences.
If your box still says it can't find any channels, just leave it on 1 channel for a few minutes while it updates itself and you should find it will be fine from then on, and with the new software update you might even find the menus a rea bit faster and more responsive.
Give it a go, you can't damage the box.
I didnt expect the prob to last this long.
