The whole darned internet ? I hadn't noticed !
I suspect you mean you can't access the internet. Or maybe that it affects the other computer as well.
Given that it doesn't work at the moment, I think you do need to reconfigure your network to conform to the norms. Modem to router then via cable or wireless to computers. Press the reset on the router to restore its factory defaults and undo any weirdness in IP or DCHP or DNS settings. Refer to the quick start leaflet or download the full manual for the router.
Check the computers' TCP/IP Properties.
Start, Connect To, Connection, Properties, Scroll Down TCP/IP and highlight, click Properties and check that Obtain DNS and IP address automatically are enabled.