Wired or wireless connection between router and PC you should be able to browse to the router's administration pages (check the manual for the
http://???). Make sure that the PC's network connection is set to obtain the IP and DNS automatically. I'd suggest getting rid of any mac clone you might have tried adding to the PC's network card. That might just confuse the router and / or the modem. Normally the most you'd do is clone the mac of the computer's card into the router's WAN settings, but strictly speaking that shouldn't be necessary.