Thanks for using the forums. Sorry to hear you are having an issue with the audio on your Slingbox.
If you aren't receiving sound on the Slingbox, it could be a few different things. You will first want to make sure that you are using the red and white audio cables from the cable box to the Slingbox. You will want to make sure they are plugged in tightly. If all the cables are plugged in, you would want to check the audio settings in your cable box. This should give you your audio back.
Hope this helps,
The Sling Moderation Team