PROBLEM SOLVED!

If you are connecting the D-Link router to another router to use as a wireless access point and/or switch,
you will have to do the following before connecting the router to your network:
1. Click on Advanced and then click Advanced Network. Uncheck the Enable UPnP checkbox.
2. Click Setup and then click Network Settings. Uncheck the Enable DHCP Server server checkbox.
3. Under Router Settings, enter an available IP address and the subnet mask of your network.
Click Save Settings to save your settings. Use this new IP address to access the configuration utility of
the router in the future.
4. Disconnect the Ethernet cable from the router and reconnect your computer to your network.
Connect an Ethernet cable in one of the LAN ports of the router and connect it to your other router.
Do not plug anything into the Internet port of the D-Link router.
5. You may now use the other 3 LAN ports to connect other Ethernet devices and computers.
To configure your wireless network, open a web browser and enter the IP address you assigned to the router.
Refer to the Configuration and Wireless Security sections for more information on setting up your wireless network.