If you successfully did a reset to the router configuration you should be able to login using the default user and pass but you must connect to the router by cable.
In some routers its possible to change the router IP address so its possible the router IP got changed after the reset.
Connect to the router using a Ethernet cable, wait until the PC recognize the connection, open the command prompt and use the command ipconfig /all
locate the gateway IP and then try accessing the rooter using the web browser to open http://gateway_ip_address
If you need help on this steps please ask, in that case post the Windows you have (XP, Vista, 7).