We've just suffered a power cut. Upon the power returning the R4 has started making a noisy whirring sound and the red light has come on along with the blue lightning symbol (don't know if that was there or not previously)

The host Mac cannot see the R4 either within the Promise utility or Disk Utility.

It sounds like the unit itself has been damaged but hopefully not the 4 x HDs inside.

Is there a way to fix this or do I need a new unit?

Can I simply remove the drives from this unit and insert them into a new one?