RND4000v2 - RND4000 NV+ v2 - Readynas Wont Switch On Boot Up

Before you buy a used NAS, you need to be sure of what version your NAS and the one you are buying are.  Many users incorrectly believe they have an NV+ V2 (or Duo V2), but really do not, and many are similarly sold mislabeled.  I recently looked at eBay and none of the "NV+ V2" or "Duo V2" listings really were V2's.

The problem stems from the fact that Netgear originally used the v2 (and v3) designations on the sticker of the NAS to indicate a minor hardware revision.  They later released an entirely different box, incompatible with your volume, and called it a "V2".  So, ignore anything on the paper stickers.  If it says "V2" on the front of the unit, it's really a V2.  An NV+ V2 is also black in color and has an external supply and a V1 is silver with an internal supply.  If your NAS (or one you are purchasing) doesn't meet that description of a V2, it's a V1 (which, of course, isn't labeled that way because they didn't know there would ever be a V2).

But your problem really doesn't sound like a hardware one to me.  You say RAIDar sees the device when no drives are installed, but not without.  Does that include when you installed the spare drive?  What does the front display say when you've inserted your volume or just the spare drive?

Can you get into the reset button menu (with at least the one drive installed)?  Since you say you did a factory reset with the spare drive, I think you can, and that's a sign the hardware is probably OK.

One thing that can be a hardware one that only affects the unit when a drive is in it is a weak power supply.  For most other things, the fact that the NAS is visible in RAIDar without drives is another indication that the hardware is fine.  In your case, a corrupt flash may be the issue, which can be fixed using USB recovery.