I believe the "streaming" indicates that your Slingbox is connected to the internet and able to send its signal through the internet to your remote computer or viewing device, such as an iPhone.
But if there is no audio or video, then that suggests to me that the broadcast TV signal is not getting into your Slingbox to be sent over the internet. Is there a way to check that the TV whose signal your Slingbox is forwarding is able to display audio and video? It might be a problem with the TV signal itself.
Since you are not able to get the audio and video signal, we recommend you to check the connections you are using between the Slingbox and TV source. If you are using the HDMI cable, you will have to remove it since it is not compatible.
The following link will provide you with further information and steps to follow in order to fix this issue.