Thanks for posting in the forums! I'm sorry to hear you are unable to get a video signal when connecting to your Slingbox SOLO.
Usually the message you are getting means your cable box is powered off. I would try pulling up the Onscreen remote and pressing the power button on that.
If that does not work, below is a link to an article from our support site that provides additional troubleshooting steps:
Hope this helps!
The Sling Moderation Team