Hi Ever,
I wish I knew for sure. I had a lot of problems installing Sonarr and looked through a great many sites to find a solution. Somewhere I found a description of installing Sonarr ‘by hand’ on a 64bit system with some instructions. Since then Sonarr works. But not very well. The program crashes often. I cannot, for instance, delete an item from the ‘Activity’ list without causing a crash. I too want to start from scratch but I am not sure what the site was I used back then 
(bookmark, bookmark, bookmark…)
Might be this one, though
Currently I’m thinking of trying again with a different OS, this time 32bit, see if that works. Unfortunately I don’t have enough time to experiment right now.
Good luck!