For a step further, also worth doing a software update (different combination of buttons but you'll find it on the web easily enough). You do lose all stored progs though.
I recently had an HD box that wasn't working properly. Had tried rebooting, software update, planner resets etc. In the end I called Sky - they said a standard call out was £65, but this included a new box if that is what was needed, then said they would reduce this to £30 as I have been with...