Press Ctrl+R type in:
cmd
then on the Command Promt type:
ipconfig
it should give a couple of parameters, locate "Default Gateway" and type it's IP Adress on your Browser.
P.S. You will need to know the Username and Password of your Router.
In most cases the IP Address is:
192.168.0.1
192.168.1.254
192.168.1.100
192.168.1.1