WNR3500Lv1 - Access Point

> Attempting to use the WNR300Lv1 as an access point. [...]

   How, exactly?

> [...] Have latest firmware uploaded. [...]

   As always, an actual version number (when available) would be more
useful than your opinion of what's "latest" today.  Probably not
critical in this case, however.

> [...] Firmware automatically gave this router the 10.0.0.1 IP address,
> [...]

   That will happen when its WAN/Internet port is connected to some
other router which is already using its preferred (192.168.1.*) subnet.

> [...] The software/firmware for this router doesn't have a Wireless AP
> select option, even though It shows "ON" in the advanced wireless
> settings.

   That setting refers to the WAP as used by the router in its normal,
full-function router mode.  "ON" is good, but it doesn't disable (or
evade) the normal router functions, which is what you want.

> [...] when I move the Ethernet line from the main router to the access
> point router from WAN to LAN, I can see the other computers, but lose
> the wireless connections. [...]

   Almost any wireless router can be configured as a WAP, but, to
arrange that, you need to make more configuration changes than moving a
cable.  For one step-by-step on how to do this, see:

      https://community.netgear.com/t5/x/x/m-p/1463500

That's written for a C6300, but the steps are about the same for any
other router (any make/model) which lacks a one-step WAP option,
including yours.