cg3000D routing function stopped working

> Routing function of my device has stopped working.

   What, exactly, does that mean to you?  It's 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 with their
actual results (error messages, ...) can be more helpful than vague
descriptions or interpretations.

   Does this gizmo have LED indtactors which indicate anything?

> Can't get access to routerlogin.net/com as device is not wifi connected;

   Does that mean that you got an error page which said, "You are not
connected to your Router's WiFi network. [...]"?  If so, then 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" should point to
your own router, but that's true only if you use your own router for DNS
name resolution.  Irregardful, you should be able to get to the thing
using its IP address, if you can determine (or guess) that.

   The User Manual for your router should tell you what its default LAN
IP address is.  Look for "192.168.".  Otherwise, you can often get it
from your (unspecified) computer's IP configuration as the default
gateway or router address (or some similar description).  Visit
http://netgear.com/support , put in your model number, and look for
Documentation.