First thing you want to do is see if you have a link light on your router when you plug in the ethernet cord from the Denon.
If you aren't getting a link light, then something is either wrong with the port on the denon receiver, your ethernet cord or the router port. Plug another device such as a computer or xbox into the same router port using the same ethernet cord and see if you get a link light. If you get a link light with the computer or xbox and not with the Denon, then you know the problem is on the Denon side. You may have a defective Denon.
Let's suppose you did get a link light with the Denon. That is a good sign. We know we have a good physical connection and the problem is probably a setting on your router or on the Denon. The reason you might not be getting an IP address on your Denon is because DHCP might be disabled on your router.
Use a computer connected to your router by wire or wireless to browse to your router's configuration screen. You do this by typing your default gateway address into the address bar on your internet browser.
Just enter the ip address of your default gateway into your address bar and it should take you right in. FYI, this is the same screen that you set up your SSID and WPA2 password.
If you don't know your default gateway, just click start and type in the run/search box CMD and hit enter . This will bring up a command prompt. Then type ipconfig and hit enter. One of the lines that appears will say "default gateway". It should be someting like 192.168.1.1.
A login page should appear and you should login with your userID and password. If you never changed the login credentials, the userID will be admin and the password will be blank.
Click on the Setup tab and then on the left column, click Network Settings. Make sure the drop down list on the top of the Network Settings page says Automatic Configuration - DHCP. Look about halfway down the page and make sure the Enabled radio button is clicked in the DHCP server section.
If you had to make any changes, click the save button at the bottom of the screen. If the settings were already correct, then you know that DHCP was already enabled.
Once you have verified that DHCP is enabled, click the status tab on the upper right hand corner. Click the local network sub tab. Click the DHCP client table button. This will list all of the devices that your router has assigned IP addresses to. Click the refresh button to make sure this screen is up to date.
Look for your Denon receiver name and/or mac address. If it isn't showing up here, then you know that your router is not assigning an IP address to your receiver. Make sure that the receiver is set to receive its IP address via DHCP.
If the Denon is set up for DHCP and you still aren't getting an IP address automatically, you may need to assign a static IP address.
Click on the Setup tab then click on Network Setup on the left column. Click the DHCP Reservation button in the middle of the screen. Find the "Manually Adding Client" section. Type in your Denon "friendly name", type in an IP address of your choosing and then type in your Denon MAC address. FYI you will want to pick an IP address that is similar to the ones assigned to your other devices. For example, if your laptop is assigned 192.168.0.100 and your Xbox is assigned 192.168.0.101 then you may want to pick something like 192.168.0.109. Make sure NOT to pick an IP address that is already in use. These will be listed on the same page so it should be easy to not duplicate an IP address.
Click add, and then click save settings. Now set the Static IP address on your Denon. Use the ipconfig command in the command prompt like we did earlier to figure out what your subnet mask is. Set your default gateway to the default gateway listing in ipconfig.
Save the settings and cross your fingers.
If none of this works, then you might have a defective Denon. Especially if other devices connected to your router work fine.