I currently have a 42 inch plasma tv and I am having problems with it working with my sky hd box. My plasma model is TH-42PZ85B. When i watch using sky via hdmi (does no matter which socket or cable) at random intervals the sound goes of and the screen goes black. To get the picture back on I either have to turn the plasma off or change av channel and then change it back. It will happen again at random intervals. How do I fix this problem?