Two Networks, One With Internet, One Without

I'm having a problem with my networks... i have 2 networks that i connect to, one that is wireless, and is connected to my INTERNET connection, and another that is connected to an Xbox and a file server through a router.

My problem is that whenever i connect to them both, i cannot connect to the Internet anymore, but as soon as i disconnect the router, i am able to access the internet again. My network center shows it as

*My-PC* -------- Multiple Networks-----x-----internet {when im connected to both}

and

*My-PC*---------*Wireless Network*---------Internet {when im connected to the wireless only}