if you haven't disconnected anything, try to turn off everything just leave the router and your computer open. check the IP Address of the machine using ipconfig /all and check the gateway and the DHCP enabled, it should be "Yes" so that you can ensure that it only acquires IP address from the DHCP server of the router, if not then set up your PC to acquire an Ip Address from the router. once you confirm, try to ping the gateway and that should respond to ensure you have a proper connection with the router.
If everything works fine, try to open a web browser and from that you should be able to access the router's config page. also check if the proxy address / settings are enabled, this should be disabled first if you use a proxy address.
as for your Xbox, there is no need for you to set a static Ip address. I recommend to set it up in Dynamic only so that you won't be bother to set up forwarding an other stuff. D-Link routers are NAT-compliant with devices such as XBox and PS3 so no need to setup for static Ip Address.