I have found, after setting up mixed wired/wireless routers to cable modem/dsl that it takes a few resets/reboots of all connected devices before everything *just* works.
Specifically the order I usually set up the router is as follows:
Get your DSL account info if you need to re-enter it after resetting the cable/DSL modem.
Plug in an Ethernet cable from a computer to the router.
Power on the router.
Load the admin web page in a web browser (Linksys is
http://192.168.1.1, D-Link uses
http://192.168.0.1). Linksys doesn't have a user name, just a password while the D-Link has "admin" as the username and no password (just press enter) - go figure.
Then I go into the Admin screens (or setup) for the LAN via the router and make sure it looks okay. I always turn off remote admin/wireless admin.
Next CHANGE the admin password on the router!!! Make sure you right it down as you may need to re-enter it several more times.
UNPLUG the cable/DSL modem from power. Typically the modems attach themselves to a particular Ethernet MAC address and require "rebooting" to attach to a different MAC address.
Next I plug in the router into the cable modem/DSL with an Ethernet cable. Power on the modem. You may need to "release IP" or "DHCP renew lease" on the *router* if you don't get a new IP assigned to the router after a few seconds.
On the Mac, open the System Preferences and go to Network. Click on the Ethernet item in the list and click "Configure..." to check it's settings. You may need to click on the TCP/IP tab and click "Renew DHCP Lease" to get a new non 168.* or 10.* IP address (self-assigned addresses usually start with these numbers). Your IP address should be 192.168.x.x generally.