ReadyNAS NV+ V2 (ARM) stuck in Boot - Normal Mode

Hello,

I am having some big troubles with my ReadyNAS NV+ V2 / RAIDiator 5.3.12

I was copying a big bunch of files when I just lost the connection to the NAS. I switched it off (normal way pressing twice the power button).

But since then, when I try to restart it just displays 'Boot Menu' after a couple of seconds and stops. Pressing the backup button I can just access the Normal option and can't move from there at all (tried reset, backup, power buttons).

RAIDar can't see it and I can't connect anymore using its IP address.

I used to have 2HDD in it used as JBOD. I have tried to remove the disks and reboot. Same issue. With only one disk. Same issue.

I would like to reflash a firmware through USB but can't find any procedure for RAIDiator 5.3 :(

Of course my unit is no more under warranty.

So I would be extremely grateful for any help.

Thanks and regards.