Thank you for posting in our online answers forum! I'm sorry you are having trouble connecting to your Slingbox after changing to Verizon Fios. When changing the router/modem connected to the Slingbox, you will need to hard reset the Slingbox to factory settings. This is done by holding down the reset button on the Slingbox for thirty seconds. Below is an article that will assist you with troubleshooting this issue.
Hope this helps!
The Sling Moderation Team