If the Slingbox has ever been set up before, you might have to perform a factory reset on the Slingbox. Check the network light on the Slingbox to make sure the Slingbox will be able to see the network that it is connected to. Here are a few articles that will help with the steps you might have to take.
- Slingbox.com - How to reset your Slingbox to factory settings
- Slingbox.com - The Network light on your Slingbox blinks or turns off