Ive got Xbox360 & for some reason LIVE doesnt work Ive done everythin theyve asked over and over again help?

I've contacted my ISP, reset my router and modem, changed my MTU settings, opened the required ports. I'm connected directly to my router. When I go through the test it says I'm connected to the network and internet and when it gets the XBOX LIVE, the last test, it just gets a red X over it. Can anyone PLEASE help me? I've been without it for too long :(