Connect your router as it was.
Using a network cable, connect you computer to the router.
If you have Windows 7 - go to the Start menu, type "CMD" in the search bar the bottom. Press "Enter"
If you have Windows XP - Start Menu, Click "Run", type "CMD" and press Enter.
This will give you a command prompt (a black screen with white writing).
Type "ipconfig /release" Press Enter
Type "ipconfig /renew" Press Enter
Wait and see if it connects to the router.
If so, then type "ipconfig /all"
Look at all the information that comes up and under the LAN (Local Area Network) connection.
Write down the IP address of the "Default Gateway" - this is the address of your router.
For instance, it may be 192.168.1.1
Type that exact IP address into your web browser and press enter.
This should get you into the Web Interface of your Router.
Side Note - I have seen many times where a router and Modem share the same IP address; if this is the case, you will have all sorts of problems. You can follow the steps above when connected to your modem directly to find out what IP address is being passed from your router.
Here is a link to an article that I wrote that helps explains Networking 101 - http://cookingcomputersandmore.com/?page_id=113