RND4210 v1 wont power on

Assuming you verified the outlet has power (UPS didn't fail), chances are something in the NAS other than the button itself has died.  Most likely the power supply, but perhaps something else.  Since it happened at power-up, the data volume is likely intact.  You could remove the drives (labeling order for re-installation) and see if it powers up empty.  If it will, one drive may be dragging it down.

There are a lot of different ways to recover the data from the NAS.  The preferred one is from your backup which, as a business device, it should most definately have had.  But assuming that you don't have one, you could move the drives to a compatible chassis (ONLY another NV/NV+ V1), replace the power suppy (and hope that's the problem), use a standard ATX supply with a special adapter externally to power the NAS while you recover the data, or move them to a current model and (with paid help from Netgear), recover the data to an external device.

Buying a used NV/NV+ is a bit of a gamble, as it will likely be no younger than yours.  If you were to do so, you should consider it a temporary thing to move the data to a new NAS.  You then might consider using it as a backup.

A few observations:-

1. This forum is not Netgear Support, although some Netgear staff contribute to it

2. Your Device serial number indicates it to be a RND 4210 V1, your footer signature states V2

4. A new Power Supply is available HERE 

5. I am guessing you don't have at least 1 seperate backup of your data, this is very risky.