You may need to hard reset your Slingbox and then set the unit back up again. If you do not remember how, have a look at the following article:
Once the unit has been reset, you will have to wait until the network light comes back on. This may take up to 2 to 4 minutes depending on your network speeds. Once the network light comes back on, go to the following setup link below to set up your Slingbox again:
Before the setup though, have a look at the following picture of the Pro-HD's inputs and make sure the audio connections to the Slingbox are running from the cable box to the Slingbox indicated by the red box outline below. If not, you will have to have the Red and White audio cables connected to have audio to the Slingbox:
If you notice that these cables are not connected here, change them to these ports and then re-setup your unit.
Hope this helps!!!
Sling Media Moderation Team