In my case, non of the recovery methods worked. i had a broken firmware because of an failed update.
i was able to boot up the qnap 212 without harddisks and need to push reset button while pushing power button for some seconds until it beeps twice. then qnap boots up with dhcp and resettet password and so an. then connect with qfinder and try firmware update with and without harddisks. it always stopped with some error that its unalbe to write firmware because of some network error. makes no sense…

in my case this worked: when you unscrew the green circuit board, theres a battery on the backside. take it out, pull the powercable and wait a few minutes. after that, put the battery back in, boot up the qnap holding reset button pushed until it beeps twice, take qfinder, connect an harddisk (sorry, data lost) an run the config assistant including firmware update.