Just thought I would drop by and share with you this article from our knowledgebase, as it pertains to your situation.
This article, despite the fact that it does not mention your model Slingbox, covers the three main reasons why you would not get video signal. I would run through the troubleshooting in this article, and if that does not work, I would try an alternate set of video cables.
Let me know if this helps!
I began having trouble connecting to my Slingbox Pro HD. It kept telling me to enter admin password. I had son reset the Slingbox and go online to reconfigure. I am able to connect , and have even had audio, but it says "no video signal".
Any ideas on how to fix?