There are a number of "standard" addresses you could try, e.g. 192.168.0.1, 192.168.0.254, 192.168.1.1 etc but the best way, if you have connected your pc to the router, is to open a cmd window by clicking on Start, then Run and typing cmd in the window and pressing Enter.
In the cmd window, type ipconfig and press Enter. After a short wait, a table of addresses will appear. The address of the router is that given as the Default Gateway.
Type this into your browser address bar and you should be able to enter the router's setup pages.