The 2 wire I tried was very tough to port forward on. The LAN worked well but never could get the SB from outside.
So when you call SB they always want the slingbox connected to the 2wire or first router coming in. Once it has been found you can move it.
Thats one thing to try. Manually port forward the SB address with the 5001 port. is another.
Reset the SB to start from scratch.
The new web interface seems to be very good for setup so it is best to use and is best on the PC side.
The setup of your ISP is one of the most difficult aspects of the whole procedure.
Bring your SB somewhere else with a different ISP and see if it will work there. Do you have any static IP addresses you can get at? They are best in my experience.
If you can get it to work somewhere else maybe its the 2wire situation. Bring it back home and reset it.
You could turn the 2wire into a bridge and hook up a regular router to the 2wire. Thats what I was going to try but they moved to comcast and it worked..
You can also find other ideas googling.
I wish you good luck and tell you that once it works it rarely falters