Netgear R6250 Smart WiFi Router how to check if it's working properly?

I woke up this morning to an internet which was down. It's been working fine since I set it up a month ago. I can, however, see all the computers on my home network: I can connect to my desktop computer from my laptop as usual. I can also see the SSID.

The modem I'm using is the Arris SURFboard SB6141.
The router is Netgear R6250 Smart WiFi Router.
My internet provider is Comcast.
Operating System is Windows 10 Home.

Here's what I've tried:
Rebooting the modem, router and computer.
I've also tried connecting the modem directly to the desktop. I get the same error.

When I called Comcast they had me repeat the steps multiple times. They also could say there's no internet outage in my area. They ran a diagnostic test and confirmed for me that the modem was fine. The Comcast phone tech suggested I run cmd and the command ipconfig/ release and ipconfig /renew.
I got the following: "An error occurred while renewing interface Local Area Connection : unable to contact your DHCP server. Request has timed out."
They suggested I contact Netgear.
I've also tried updating the router's firmware. It wouldn't work. No internet connection.

How can I continue to troubleshoot?