Weird light inside my RNDX4410

My NVX is in storage, so I have no way to see if that LED is normally on (I think it's supposed to be green).  I suspect it indicates the unit is failing the Power-On Self-Test.  Obviously, you have some power or the LED would not be illuminated, but one or more of the voltages may have failed, or it could be something else.  You could try a power supply replacement or powering on via an external ATX power supply and an adapter cable, but that would just be a stab in the dark based on the most typical failure.

Do you have a current backup of the data?  I frankly don't think fixing an NVX is worthwhile, especially without a more compelling indication of the cause of failure.

If you need to recover data, you can move your drives into another OS4.2.x unit or StephenB can tell you other methods of recovery.  An Ultra4, Pro4, Ultra6, or Pro6 would be good choices since you can convert them to OS6 once you recover the data.  If the unit you buy has already been converted to OS6, you'll have to use a scratch drive and convert back to OS4.2.x.