Are you sure you haven't turned-on 'Renderless-mode' ?
(Menu->Channels->Renderless Mode (CTRL+K) )
This results in displaying no video in DD.
Also, check if you have the required (audio/video) codecs installed and configured. (ie. no red backgrounds in the codec pull-down-menu's, this indicates codecs are missing or not suitable for that particular kind of stream)
(Menu->Options->Video (CTRL+G) )
Hope this helps
(message edited because of explanation of menu's)
Thx I will check it all. And I am using the shark007 codeck pack for win 7.