Nighthawk XR500 firmware or hardware issue?

My Nighthawk XR500 isn't working after a power outage--the device is protected by a UPS, but the UPS hibernated my computer and then powered off, so perhaps it took a hit.  I tried to log into the router, but my browser said it couldn't find the 192.168.1.1 location due to no DNS server.  I saw the modem had internet access, so I tried pushing the XR500's reset button, but nothing happened.  I tried rebooting the modem, waiting, and then rebooting the router.  Then I noticed that the power light was flashing green, which suggests a firmware issue.  

So I followed the instructions to update the firmware following directions for using the built-in TFTP on Windows 10.  Except the power led does NOT flash red during startup.  Instead I have the following behaviors:

With one or more devices on Ethernet ports, repowering the machine causes the power led, usb2, and all Ethernet lights to all flash once in unison, with all leds red EXCEPT the green light on the USB2 port (there is nothing plugged into either USB port), and after that the power goes solid red and active Ethernet ports flash green, then the power begins flashing a steady slow green pulse while the Ethernet ports look active (but the computers cannot connect to the router).

With all devices unplugged from the router, the first configuration with the six lights flashing together once occurs.  But after that, the power led is STEADY RED.

So is this more likely to be firmware or hardware, and is it fixable?