I'm losing this battle.

[McLaughlin]

In my never-ending quest to fix my lag issues on my 360, I've proved my own hypothesis wrong. It would appear that when my PC is off, my 360 seems to work fine ("seems" being the operative word).

Someone up there must really hate me, but I can't figure this crap out, and I'm going bonkers. If I have a problem, I have to solve it, or it eats away at my soul until nothing is left.

So, either it really is my router, or I've run in to a string of coincidences while testing my connection.

Why the heck are connection issues to bloody hard to diagnose?

[Brainwrecked]

I had a friend on XBL that had the same problem you had. While the cause is still unknown, it remains that one PC and his XBox 360 cannot play nicely on the same local network.

Two things I can think of that maybe you'd like to consider:

The PC might have some software installed that is taking up one of the ports the XBox 360 wants to use (http://brainwreckedtech.wordpress.com/2008/03/08/more-ports-on-xbox-live/). The first 3 ports and XBox 360 tries to use are 3074, 15980, and 24687.

The PC might also have software that's sending out a bunch of traffic on the local network. An ill-behaved app can easily slow a local network to a crawl if it sends broadcasts as fast as it can.

You'll need network monitoring software (and a third computing device) to analyze the situation. Or you could borrow a friend's router (or buy a new one) and see if things play nice again.

[McLaughlin]

I'll have to check today, but I think my router has become unable to properly handle traffic. I think that as long as there's more than one device online, everything slows down. It's just more noticeable on Xbox Live.

I have an older router I could hook up, but I replaced that one because even though my NAT was open it would not connect me to 80% of games in Perfect Dark Zero, Gears of War, ect (any game that doesn't have Matchmaking, essentially). I even put my 360 in the DMZ and it still didn't fix the problem.