It seems that you have some issues while trying to set up your Slingbox with a Cisco DPC3825 router.
First, you need to verify if the Slingbox is able to communicate with your router / network. If the Slingbox does not show any light on, the issue might be related to a faulty power adapter.
I recommend you to check the following third-party link in order to get the steps by step instructions about how to set up your Slingbox for Internet Viewing with the Cisco DPC3825 router:
Port Forwarding SlingBox on the Cisco DPC3825
If the Slingbox shows no lights at all, I recommend you to check this link:
Hope this helps!