Most domestic cable ISPs have the cable modem configured to recognise only one client computer by the MAC address of its network interface.
Once the cable modem has learnt the MAC address of the first computer that talks to it, it will not respond to another MAC address in any way.
Thus if you swap one PC for another PC or a router, the new router will not work with the cable modem, because the router has a different MAC address to the PC.
You need to power off the Cable Modem, Router, And the Computer, connect the Cable modem to the router via the Ethernet port to the router wan port connect a second Ethernet cable from port 1 on the router to the lan card on the computer.
Wait 30 minutes
Power on the cable modem,, and has rebooted and gone fully online again indicator lights settled down, Power on the router and wait until has fully rebooted.
Power on the computer and wait until it is fully rebooted
You should now able to access the router via the browser
But there is a limit on the number of MAC address changes, which are permitted within one 4-hour period