If anything has changed in your network, you would have to factory reset the Slingbox. Deleting the Slingbox off your account does not do the same thing. If the Slingbox was deleted but not hard reset you would have an issue like that. After the reset, it should be like it was a new box again. Just go to newwatch.slingbox on the same network, and set the Slingbox up. If you still can not start the set up, I'll have some articles below that will go through some trouble shooting steps that might help.
- Slingbox.com - How to reset your Slingbox to factory settings
- Slingbox.com - The Network light on your Slingbox blinks or turns off
Hope that helps!