If you've done a reset (pressed and held the inset button in the rear of the router), then the IP address is 192.168.1.1.
The problem is probably that your computer is using an IP address other than the range 192.168.1.2 - 254. If your computer is using an address of 192.168.2.x, or 3.x, etc, you will not be able to connect to the router.
You need to change the IP address of your computer first. You do this by opening Start-Control Panel-Network Connections.
Right-click your network card (local area connection), and select properties. Then select Internet Protocol, then click Properties. On this page, change your IP address to 192.168.1.50 (or any IP other than 192.168.1.1, and make sure you don't use the same IP of any other computer on that network).
Once you do this, click OK until the two top windows are closed, and then X out of the last two. The computer may pause when you click OK the first time.
NOW you should be able to connect to the router using 192.168.1.1.
Good luck!