R6350 Not Connecting to Spectrum Internet

> I just had my spectrum modem set up, [...]

   Not a very description of anything.  What is it?  To what is
it connected?  (Hint: If a device has different types of ports, then
"connected to device" is not enough detail.)

> However my nighthawk R6350 router when plugged in via the same
> ethernet cord is not able to connect to the internet. [...]

   What's at the other end of that "the same ethernet cord"?  What,
exactly, are you connecting to what, exactly?

   A vague description of what some device does _not_ do is less useful
than a clear description of what you do, and what _does_ happen.

   "not able" is not a useful problem description.  It does not say
what you did.  It does not say what happened when you did it.  As usual,
showing actual actions (commands) with their actual results (error
messages, LED indicators, ...) can be more helpful than vague
descriptions or interpretations.

> [...] The only thing I haven't done is firmware update, [...]

   A firmware update might be desirable, but is seldom imperative in a
case like this.

   "only"?  What about this seldom-used (but occasionally effective)
technique?:

      https://en.wikipedia.org/wiki/RTFM

   Visit http://netgear.com/support , put in your model number, and look
for Documentation.  Get the User Manual (at least).  Read.  Beyond the
basic set-up instructions, look for the LED descriptions and
"Troubleshoot".

> [...] The wifi connection works fine on the LAN, but I don't know of a
> way to send a firmware update in reverse.

   I don't know what "send a firmware update in reverse" means.

   You could download a firmware kit to your computer while it's
connected to the Internet, and install the firmware when your computer
is connected to the R6350.  But I doubt that that would help.

> I am not able to log onto routerlogin.net, because I have to be wired
> in directly to the modem to access the internet at all, and when I am
> connected to the router via LAN there is no internet connection.

   There's that "not able" again.  Did you try?

   "routerlogin.net" should point to your own router, not to some remote
site on the far side of the planet.  You shouldn't need an Internet
connection to talk to your own router.  What does the User Manual say
about this?  "First configure your router so that you have an Internet
connection, and then you'll be able to configure your router"?