Do you have a computer connected to it with a wire? Go and open up command prompt and type ipconfig /all to see if you have an IP address from the router. The default gateway is the IP address you'll use to get to the router configuration page.
Open up IE and type that IP.
If you are using Firefox you might have to specify the port like for example
192.168.1.1:80 or 192.168.1.1:88
If anything doesn't seem to work, reset the router back to factory default and follow the manual, it'll tell you what IP to use.