> [...] my new ISP gives me RJ-45 as input.
It would be nice to have some idea what's on the other side of that
RJ45. Or, who your ISP might be.
> After reading some pages about how to make my modem+router as router
> only I "disabled the DHCP server" option.
With my weak psychic powers, I don't know what you read. As I read
the User Manual, a DGN1000v3 has no WAN port, so you would seem to be
using it as a wireless access point (not as a router), which would be
consistent with disabling its DHCP server.
> 1. I can connect only one device at a time. (I have my PC hardwired to
> the Modem, if I connect a mobile device via Wi-Fi it disconnects the PC
> and then connects)
What are these devices getting as their IP addresses? With the DHCP
server of the DGN1000v3 disabled, this would need to be assigned by the
ISP or some mystery device behind your RJ45 connector. If the ISP or
mystery device is acting as a bridge, then your devices may be getting
your (single?) public IP address, and this can be assigned to only one
device at a time.
> 2. I cannot login to my router home page (The default gateway returns
> no connection found, [...]
What (approximately) was that "default gateway" address? Something
at your ISP, or something local (like 192.168.x.y)?
> [...] www.routerlogin.net says that "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" 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. In your
case than may be difficult.
Getting the useless error page could happen if you're connecting to a
bridge(-like device), and you end up using a real-world DNS server.
> [...] Netgear genie doesn't login at all)
Ever helpful, Netgear uses the name "Genie" for more than one thing.
Netgear routers have a web-browser interface called "Genie", and Netgear
offers application programs for various computers/pads/phones, which are
also called "Genie".
In your case, there might be no way for a Genie app to communicate
with the DGN1000v3. If the DGN1000v3 is acting as a wireless access
point, then I doubt that it would have a suitable LAN IP address.
If the DGN1000v3 has nothing which would act as a WAN port (which is
how I read the User Manual), then you might need to replace it with a
router which does. Some of the newer/better DSL modem+routers (like,
for example, a D7000) have an Ethernet WAN port (either a dedicated one,
or else one of the LAN ports can be configured as a WAN port). You
could use such a device as a plain-old router, ignoring its DSL modem,
but the DGN1000v3 seems not to be one of those. Of course, a plain-old
router (with no built-in DSL modem), like, say, an R7000 should also
work.
But knowing nothing about your ISP or its equipment, all of this is
based on guesswork/inference.
