Before anything else, you need to
upgrade the router's firmware.
Turn off your modem and pc;
Connect modem to router and router to pc;
Power up modem and wait for the leds to settle;
Power up router and wait for the leds to settle;
Power up pc and check you Network Connections.
Shouldn't be any need to enter username or password, dhcp settings should be default and there's generally no need to specify any MAC codes.