Disconnnect while gaming

Hi folks. I have been having a new problem lately. In the middle of a game, I will suddenly lose internet connection. When I close the (frozen) game, to desktop, I find that I am no longer online. The only way to reconnect, is to reboot my computer. Then, I stay connected.

This ONLY happens while gaming.

I play left for dead 2, and team fortress 2. It has happened in both games.

I have a modem, running to a wireless router. But I use the router as a splitter. One line runs from router to me, the other line runs to another room. That room's PC does NOT get disconnected. So it is between the router and my pc. Or on my pc.

Does anyone know what might cause this?

Thanks in advance for any help. :confused