Look at the sky box - do you have a green light or is it amber or red?
If its not green find the sky remote, press sky then press the on/off button or tv guide.
If it is green, on the tv remote press source - assuming your tv and sky are connected by hdmi cable - if you have more than one device connected to the tv by hdmi, try each hdmi option in turn.
It is possible that you have put the sky box to sleep with the tv remote - as the tv remote is suposed to work the sky box as well - althoug I find that it only does so when you don't want it to (I have a Samsung as well!)