Accessing ReadyNas RN31200 without networking

Are you also observing any issues turning the unit on and off?  I ask because the NIC components and power-on circuit use the same power source, which remains on, even when the rest of the unit is off.  But the fact that those components remain on can also be an issue if the unit was ever left where it was plugged in and the temperature got very high.  I  don't think Netgear (or PC manufacturers, many of which do the same thing) warn you about that.  Many users assume it will be OK if it's "off".

A nearby lightning strike can also be a cause for failure of NIC components, especially if the incoming network connection and power have different ground points.  I have two DuoV2 units with lightning damage (I bought them that way for parts), though not total loss of Ethernet.  Neither will negotiate a proper connection on a "green" switch or over a long cable, but you can see LED activity as they try.

If you see absolutely no activity on the LAN LEDs, then the problem is not in the flash memory, it's the NIC or power distribution and is non-repairable.  The process is here: How-do-I-use-the-USB-Recovery-Tool-on-my-ReadyNAS-OS-6-storage-system if you still want to try it.