I'm not familiar with your router. Since it sounds like you're rather new to home networking, I suggest to get one of the known xbox compatible routers:
compatible list.
Given the information you gave, I would set the 360 back on dynamic again. I thinking you're don't have correct DNS settings right now. I would then trying port forwording, then the DMZ zone. Turn on the UPnP if the router has it. You can always try unplugging everything for about five minutes, then connect everything in this order--modem, router, 360--making sure each device is up and running before turning on the next.