Cannot access routerlogin.net

> [...] You are not connected to your Router's WiFi network. [...]

   Welcome to what may be the worst error message in the world.  For an
explanation, try:

      https://community.netgear.com/t5/x/x/m-p/1365830

   Briefly, the idea is that "[www.]routerlogin.net" (or ".com") should
point to your own router, but that's true only if you use your own
router for DNS name resolution.  Regardless, you should be able to get
to the thing using its IP address, if you can determine (or guess) that.
Normally, that would be something like "192.168.1.1", but it could be
different.

> [...] The IPv4 IP address is 76.101.xxx.xx. My Default Gateway is
> 76.101.xxx.x

   Ok.  That's your external/public (Comcast) address.  You should get
that if your computer is connected directly to your cable modem, but not
if it's connect to a NAT router (like a normally configured R7000).
That would explain why "routerlogin.net" led you to that
misleading/useless error page.  (Although in this case, its message may
have been closer to the truth than it usually is.)

> [...] This is a sarcastic remark!

   No, it really isn't.


> It is time to return/exchange the router.

   It may be, but I'd run one more test first.  Disconnect the R7000
from everything but power.  Cable your Windows system to a LAN Ethernet
port on the R7000.  Don't involve the modem.  Reset the R7000 one more
time.  If/when it comes up, start the computer.  Verify the physical
link status from the R7000 port LED indicator (and/or any suitable LEDs
on the computer).  When it comes up, do one last ipconfig command.
(That should also show a "media" status.)  If the router is really bad,
then I'd expect to see a "self-assigned" address (169.254.g.h).  If
(through some miracle?) you get "192.168.1.X", then you can worry about
what happens when you try to connect the other equipment together.