Why does turning my modem off for a few minutes and then turning it on again (power cycling) fix the DNS Not Resolved problem?
Some modems are configured to “remember” the MAC address of the device that is connecting through them. By power cycling the modem, it “forgets” about your PC and will let your Xbox through. Generally, this occurs because your ISP is only allowing you to connect with one network device at a time. You may want to ask your ISP what options they offer for simultaneously connecting multiple devices.