1.) look for blinky lights on the modem
2.)(assuming you’re running windows) hook directly into the modem with computer “Start>>run>>“cmd”>>ipconfig” if you have an IP etc, unplug computer from modem. plug in router, plug computer to router
3.)go to routers settings page (could be 192.168.1.1, thats the norm for new linksys anyway)
4.) see if router has an IP from the modem. see if you have IP from router (start>>run>>blah blah)
If you have an ip from the router and the router has an ip from the modem, but you get no connectivity to the internet router/NIC/modem is fucked.
if you have Internet, relax and enjoy.