Why isn't Xbox Live working?

Recently, my dad turned the wireless off of the internet, so he could get most of the bandwidth for something. After that, I've been unable to get on Java chat sites. Not a big deal. When I got an XBox for Christmas, and tried to connect to Xbox live, the troubleshooter said it was a matter of MTU. I asked my dad to take a look at the settings, and it said the MTU was at 1500. Higher than the minimum of 1364. Help?