How do you open your NAT for Xbox Live?? (Belkin Router)?

I have followed all of the instructions I can find on Youtube but once I get to where I type in my IP address and save it, it won't save. The page just acts like its loading and it doesn't do anything. I have tried resetting it but it still won't save the changes and my NAT is still closed on Xbox. Does anyone have any ideas on how to fix this? I greatly appreciate any help :)