I've just got a blank screen when I switch my Sky+ box on.

[SianAS]

My TV is recognising that my Sky box is on.  I've turning the box off at the socket for a few minutes but that didn't work.  I'm not getting the usual message that the box is initialising either!

[caesarome]

Have you tried using your TV remote to cycle through the channels ?

[Mark39]

Turn off both your TV and your Sky box at the plug. You'll need to leave the Sky box off for at least 4 minutes for it to carry out a complete power on reset. 

[SianAS]

Tried both suggestions but it still didn't work 

[Mark39]

Does the power light on the front panel go green when you turn the box on?

If it does, try disconnecting the cable between your Sky box and your TV, swap the ends over and plug it back in (make sure the Sky box is turned off at the plug when you do it).