Im assuming you just have one router and everything is hooked up through that.
Did you test the connection of the xbox to PC?
Do you have windows medai player 11?
If you do, you need to enable sharing which is
Go to Tools >> Options >> Library >> Configure Sharing >> (tick the box) Share my Media
Also when you go to share files. Your computer should see the xbox. Allow this device.
Make sure the right services are enabled. Certain services are needed for sharing to work.
To do this, click Start >> Run >> Services.msc (Alternatively, go to Control Panel >> Adminstrative Tools >> Services)
A window will open with a long list of services.
Find HTTP SSL, and make sure it is enabled and started. If it is disabled, Right click it >> Properties >> Startup Type: Automatic
Find SSDP Discovery Service, start, and enable it the same way as the above (right click)
Find Universal Plug and Play Device Host, start it, and enable it.
Finally, find Windows Media Player Sharing Service, and start and enable it
I hope this helps. If this isnt your problem, I still may be able to help.