why can i connect to xboxlive and internet at the same time?

The problem is that I cant connect to xboxlive and internet on my computer at the same time which is a problem because my father and I are on both all the time.
The catch is that I can access xboxlive when he is not on the computer but i have to unplug the modem wait 10 seconds then plug it back in and afterwards I can access xboxlive as long as the computer is off.
Then to acces the internet on the computer, we must repeat that same process.
Please help me fix this problem.
Any additional information you might need to know like, my internet service which is timewarner, im using wireless connection, and the brand of wireless router is belkin.
Thanks.

buy a router and plug the computer and the xbox into that, or u could even by a wireless linker for ur xbox and have it connect to the wireless router.

Thats what I did too. But that part for the XBox was 100$. But hell
everything is 100$ anymore. My router runs two xboxes,two laptops,
and a desktop which is plugged into the router. You can also get a wireless card for your PC and you will be totally free.LD