You need to post more information about the problem.
Do you have no audio at all, or is it too soft or too loud?
Did it just stop working, or is it a new setup?
What source (make, model) is feeding the Slingbox?
Have you tried another source?
Does your source work properly with a TV or A/V receiver?
Using analog or digital audio inputs?
What device are you using to play the Slingbox video?
Can that device play other video content with good volume?
Have you tried another playback device?
Thanks for using the Slingbox Answers Forum! I'm sorry to hear you are unable to hear audio when connecting to your Slingbox PRO-HD.
Below is a link to an article from our support site that provides some troubleshooting steps:
Hope this helps!
The Sling Moderation Team