Thank you for posting to the Forums. Have you tried to connect another a/v source to the Slingbox? Have you tried to connect the set top box directly to the TV to make sure the ports on the set top box are still functional?
Below I have provided a support article that will walk you through some troubleshooting steps.
If this doesn't resolve the issue, please feel free to reply back to this post and we will see what we can do.
Hope this helps,
Sling Media Forum Moderation Team