Can I access my Xfinity router from another computer?

Yes you can access it from any computer that is connected to that router (be it by wire or over your wireless network). To access your router open your internet browser, in the URL bar type 192.168.0.1 once you have done this you should be prompted for a username and password, now this can vary from router to router but you can try a username: admin and password: 1234

Because there are a few different types of routers that are available from Comcast this may or may not help you without some more information about your router, primarily its model number.

One pc is for alway linked to the one router, you can't use another pc to access that router, not every, do not even thank about it.

To use another pc you will need to buy another router and maybe even a new Xbox 360.

And this time make sure the pc likes the xbox 360, introduce them first before you connect them together..

Yes, enter 192.168.0.1 in your URL bar in your browser. If a prompt comes up for a username try "admin" with no password. It should take you to your router configuration page.