|I'm guessing that's either a modem and router you have, or it's a combination unit (ie: modem/router/wireless access point all in one unit) and you're trying to connect to the router's management interface.|
Reread the manual for the router to ensure you're trying to connect to the correct address. Make sure you're plugged into a LAN port from your computer when attempting to connect to the management interface. If it's the correct address and port and still no luck, you may have to reset the router to it's factory defaults. How to do so will be in the manual. If you still can't get into the management interface, your router may need to be replaced.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.