Thank you for posting in the Answers Forum. I see, you're having trouble connecting your Slingbox M2 to your cable set-top box. With the information provided, it shows that you will need to connect composite cables (Standard Definition) from cable box to Slingbox. Below is a link with information on how to connect your Slingbox M2.
Composite inputs (RCA connection)- The white is for the left audio, the red is for the right audio, and the yellow is for video.
Sling Media Support