Hub can't update

After the last update my C7 started to display Error 500. I tried to revert to the previous firmware version, but the hub crashed at 10% and now it won't start, with the led lit in blue. The diagnostic tool is able to find the hub, but neither a soft reset command worked - I waited for more than 30 minutes, and nothing happened. I already tried to set the time too.

UPDATE: just a full reset solved, but now I'm stucked on the previous firmware version and all update trials end with a message "download failed" after a try to extract the downloaded file.

Thanks in advance for any support!