No more signal at the sky box?
Is the incoming coax/F plug routed through anything else before the Sky box? Check that first, and there is power to it if amplifier or distibution. Some systems route the incoming coax through it before the Digibox.
Sky powers up but has "No Signal" displayed on screen .. right?
Try a digibox reset ...
Follow this ...
http://www.ukfree.tv/....php?faqid=1107051203