I'm sorry to see you are having a "no video" error message while trying to stream your Slingbox. This may have to do with cable setup and/or faulty cables. Sometimes even the type of cables you are using may not be compatible to your cable box or receiver and may cause what is known as a SOC (Selectable Output Control) issue. Since you were not specific on what Slingbox you own nor the cables you are using, I will post a link below in regards to the Slingbox M1/M2, 350 and 500. Please read the article to ensure a successful video connection.
Sling Media Support