I understand you are having difficulties getting a video feed out of your Slingbox. Have you tried configuring the Slingbox to a different audio/video source to see if you can get video when using a different source? I would recommend reconfiguring the Slingbox with it attached to a DVD/Blu-ray Player or similar device so that you may be able to determine whether or not the issue is with the Slingbox, A/V source, or the cables themselves.
Here is a helpful link to assist you in the reconfiguration of the Sllingbox unit:
I would also recommend performing a hard reset on the Slingbox as a troubleshooting step for this particular issue:
Hope this helps!
Sling Media Forum Moderation Team