Open browser and you need to type
http://192.168.1.1
If it is not working type next IP
http://192.168.1.2
Again If it is not working type next IP
http://192.168.1.254
Which OS you are using Windows XP? 2000? Linux? if all of the above IP failed then we need to find out Router IP but i guess 192.168.1.1 should work for you.