Thank you for reaching out to us using our online Answers Forum. I can understand the frustration when you cannot detect the Slingbox with a new modem. I would be glad to help you solve the issue. What you would have to do is configure the unit on the network. You would start this process by resetting the Slingbox to factory settings. Then going to our online setup website and configuring it.
Here are links to help out:
Hope this helps!
The Sling Media Moderation Team