If the network light is blinking, the Slingbox can't find the router. Port forwarding and firewalls should not be causing that problem, they affect traffic moving to/from the internet. Your problem is inside the house on your local network.
Assuming your ethernet cable is good, doing a hard reset is the normal way to fix this. You mentioned that you have done that, but are you certain it was successful ? I suggest you try again.
Here's a support doc on that:
The short version is from a powered-on state, poke and hold the reset button for about five seconds. Keep holding, the lights will blink quickly, then slowly. Let go of the button when you get to slow blinking. It can take awhile for the Slingbox to startup, around 30 seconds or so. If successful, you should have a solid network and power light in under a minute and Setup Assistant on your computer can take it from there.
Hope this helps,