I've managed to put my synology back up again. I've been running out of time to deal with this situation and I had to backup all the data that I had there for security reasons. Anyway, I took the hdd out and put in an external case, connected it to my laptop (running Linux), formatted the first partition (around 2GB) and put it back inside Disksation. It booted
and said that lost configurations. So, I've downloaded (again) the version it had before, the 4.0-2198, and loaded without a hassle.
Obviously it lost all the configurations, but hey, all the other 500GB data was intact
It was a quick workaround, hope it helps anyone.