Is this happening with just the cable/sat box, or is this on all inputs?
In some cases, the picture not being present (while the audio is) is usually a symptom of HDCP (copy protection), and can be fixed if you call the cable/sat company and have them reset/refresh the box. This is a software process that can often be done over the phone.
If it's happening on all inputs, I would recommend either working with your retailer to have it exchanged, or with Samsung to have it serviced - whichever is best for you.
I have just purchased a Samsung 58" Plasma Panel model PS58B850Y1F. Occasionally when I turn it on, there is sound but no picture. This usually happens when it has been on for a while, and then turned off and on again shortly after. I haven't noticed it happen when the panel has been off for a while, and in fact the only way I can rectify the situation is if I leave the panel off for a while before turning it back on.. like it has to cool down or something. The panel will respond to the remote when the picture is not there, so I can change channels, inputs, etc., but there is no display from the remote (ie. menus, info, etc.,); the screen remains completely blank. Also there is a green LED constantly flashing from within the panel. The light from it can be seen through the perforations at the rear, but not visible from the front. Hoping someone can help with this. rgds, Peter