Thank you for posting in the forums! I'm sorry to hear you are having trouble connecting to your Slingbox PRO-HD. It sounds like you need to reset and reconfigure the Slingbox.
Whenever you change the router or modem the Slingbox is connected to, the Slingbox needs to be hard reset to factory settings. After this is done, you will need to reconfigure the Slingbox.
Here is a link to an article that explains how to hard reset your Slingbox:
Below is a link to where you need to go to reconfigure the Slingbox:
Feel free to reply if you are still experiencing issues.
The Sling Moderation