Hi Claire,
i'm having the exact same problems.  TV screen is black however there is still sound.  Also sky HD customer.  It's been happening now for a few hours and doesn't seem to be showing signs of stopping.  We have previously repaired our tv when it clicked over but wouldn't turn on from standby.  This is a new problem.  Don't think i will be buying samsung again!!  
Have you managed to sort your TV out?
Thanks
Gemma
                
 Gemma
                
 April 2010