First check for the physical connections between the computer and the router. There should be a cable (cat5 or above) running from one of the LAN port of the router to the Ethernet card in the computer.
If the computer is wireless, it should be associated to the Router/AP.
Check for any firewalls (Mcafee, Norton Internet Security) on the computer, which should be disabled.
Check for an IP Address on the computer in the range of the router i.e. 192.168.2.x (x can range from 2 to 254). The router also assigns an automatic IP address to the computers in the range 192.168.2.x (x can range from 2 to 100). For instructions on how to check the IP address on the computer, Refer to Article 13.
If you are not getting an IP Address on the computer from the router you will need to manually assign an IP Address to the computer.
You also need to restore the Internet Explorer browser to its default settings.
Go to Control Panel and click Internet options. Select the Program Tab and click on Reset Web Settings.
You should be able to get the router's configuration page if the above instructions are followed in order.