Oh poo - I just ducked out of writing all this up - I'll do it this once and clipboard it.
Go Start>Run and in the Open box, type cmd /k ipconfig /all including all the spaces. In the black form that follows wil be an entry named Default gateway and you need to note the numeric code beside that entry - something like 192.168.2.1.
Type exit to close that form then open Internet Explorer. Enter the code into the address bar as though it was a web address and you'll then face a login form, requireing a login name and password. Most routers will let you in using admin as the login and password or admin as the password. If you get in, setup pages will appear - several, in fact. The router settings are quite important and there are several you won't want to mess with.
Some routers carry the default IP address (frequently 192.168.0.1 or 192.168.1.1) on a label on the case. Otherwise see literature which came with the router or download the maker's user manual.