ReadyNas Ultra 2 Bootmenu selection not working

The data are mostly all of our family pictures from the last four years, I thought them to be crucial enough to have them mirrored on two disks but not to buy another NAS for 500€ just to have a backup. I never experienced the loss of an applience yet, only of single disks, it was probably naive from me to think that only the disk can fail and the netgear NAS itself not. For decades practically all my network gear is from netgear (hence the name? :D) and neither my switches, APs nor this NAS box have let me down until now.

However, I had in fact problems before. I was on a weekend trip and when I returned home I couldn't access my files on the NAS. I rebooted it and the shares could be mounted again. I deleted 4-5 old files I didn't need and when I tried to delete another file the NAS network went offline. This was reproducable, after rebooting the NAS the shares became visible again, directory listing worked on the PC as well as on the media receiver I use to access it but when I tried to access some individual files the NAS would vanish from the network again, WebGUI under /admin couldn't be accessed either. Reboot, rinse & repeat. I could use the WebGUI as long as I didn't try to access the files on the shares, I checked all the log files and there was no error reported, everything was green.

Then I've got the Email that a new firmware is available and I figured that it might help, resulting in me registering on the forums and opening this thread...

According to the manual it does boot into the boot menu, all LED are lit, I just can't switch the mode. I tried as you suggested and removed both disk, now this happens:

- NAS is power-off, I press the reset button on the back and while pressing it I power it on, keeping reset pressed

- When both disks LEDs and the backup LED are lit (yellow) plus the Act LED (blue) I release the reset button

- Now I should be able to cycle through the options by pressing the backup button but when I do this, both disk LEDs and the backup LED are turned off after a single click, nothing else happens no matter how many times I press backup.

- Without rebooting, when I press the reset button now in this state the three LEDs are lit again. Press backup they turn off, press reset they are lit, repeatable infinitly.

Any idea what's going on? I would guess the OS got seriously damaged during the update and I think USB Boot recovery is my only option right now. Do you happen to have a link where the procedure is described or any other tipps on what I could try?

Many thanks!