A lot of routers have a small button on the back, you can hold it in to do a reset of your router, which should set it back to stock settings as though you'd just bought it. Then you can reset it and test. If your connection does not work after that, you may need to look at a new router.
Thank you for your answer - strangely, it started working again without anything being changed. I don't believe it is the router, because the desktop, laptop, and PS/3 all work and worked fine. It was only the XBox that quit and it was picking up the neighbor's network instead, just fine.