Why can't I connect to xbox live sometimes?

When I go to test the problem it always gives me a different problem, such as my MTU settings. Well my MTU is way above 1364 (1500) and I reset my router but it doesn't work! Also when I play a game other than MW2 I seldom connect to xbox live. With MW2 sometimes it works, but sometimes it doesn't. I found that if I stand in front of the router it has a better chance of connecting.Wtf is going on?