thanks for the info,
i think if the power light does not become green at all (even with or without any drives inside) then it could be a hardware fault.
edit: chassis, psu parts,
if you are in warranty, you could create a support ticket for the problem you have, though if your mini is old then you might need to raise a one-time paid ticket with the support team ( if they can diagnose a bit more and hopefully sell you a replacement part/s? ).
the slightly better news is that so far, it seems as though the drives themselves could be ok, (because usually if it is a problem with the disk pack drives, then the hardware will still boot up and be found by dashboard, but in your case it could be the main chassis, or the psu - or possibly both). if the disk pack is ok, then a possible option would be to try migrating the disk pack into a replacement drobo mini via the migration options here:
and i believe you also get some migration assistance too in case you get stuck via here: