No Internet Through the Router.

Unable to go online from the router.
These steps are applicable for Routers only [like WNDR3300, WNR3500, WNR834B and WNR854T] not for Modems.

Step 1 : Disconnect the computer from the router and connect it to the modem.
Ensure that the computer is not assigned a static IP Address.
Turn the computer OFF and the Modem OFF.
Turn ON the Modem, than the Computer.
If you are able to go online, good.
If Not, Contact the Internet Provider.

Step 2 : If you are able to go online from the modem, follow these steps :
Connect the computer back to the router and the router to the modem as before.
Check the Internet LED is lit. If it is not, troubleshoot light status, as explained in the router manual. Check the LEDs for the ports with cables are lit. If not, move the cable to a different port. If there are still no lights, then troubleshoot light status, as explained in the router manual.

Step 3 : Power OFF the router and power it ON aftre some time [say 10 seconds].

Step 4 : Try Going Online. If still you cannot connect to the Internet, TryResetting the router as explained here.

Step 5 : After resetting the router, Open the setup page and configure the router yourself or you can try the SmartWizard.
SmartWizard helps the router discover whether you have a static or dynamic IP address, and whether you are using PPPoE to connect to your ISP.
If Dynamic IP Address is discovered, its good. If PPPoE or Static IP Address is recovered, you need to configure the router with the ISP settings yourself.

Step 6 : Now turn the Router and the Modem OFF. Turn On the Modem first than the Router.