I know this is going to be supposition and guesswork but here goes.
We have/had two QNAP NAS devices a TS-464 and a TS-431Xeu.
In October, we performed a firmware update. The 431 never came back up. When rebooted there are now no POST beeps even.
The drives (4 Toshiba N300 18TBs) were moved into the 464 which booted with them and ran fine - for two weeks. A couple of days ago, the NFS connection to an ESXi host went down. I was able to login to the management interface of the 464. When I tried to open the storage control panel, it appeared on the taskbar but the window never opened. I selected reboot in the management interface and it shutdown services and sat with the spinning “shutting down” screen. It never came back. After an hour I shut it down by holding the power button. It is now just like the 431 before it. Fans spin up and quiet down and then no POST beep, nothing. 4 green drive lights and flashing network light.
I have tried booting both devices without disks and the same result - no POST beeps, no ip address obtained.
So - it feels to me that since the HDDs are the only thing in common, that one (or more of these) is the cause of the problem - does the forum concur? Or is it possible this is just a coincidence?
Both NASs are serviced by an online UPS.
We also now have a TS-873Aeu-RP running the ESXi hosts