when you say a bridged connection, what exactly do you mean? do you have a router/switch that connects your computer and xbox to the internet modem?
your computer and your xbox have to be on the same LAN, which means they need to have very similar IP addresses. try this: turn on your xbox, go to system settings > network settings, and get the IP address. Then, on your computer, right click on your connection icon down by the clock, then select open network and sharing center. next to "connections:" click on that connection - it could be Local Area Connection or wireless connection. a dialog box will pop up, then click details. next to IPV4 address, get that IP address.
these IP addresses should be on the same network, meaning they are generally 192.168.1.x for standard routers. if they don't have the same first 3 sets of numbers (aka 192.168.1), you have a problem with your bridge/router. try restarting your router, then compare IP address again.