Three hours of debugging the program.
I also wrote a thread in a forum to ask for help explaining all the test I made.
My database is working in Sql Management Studio but not in the code. It done well only using the trusted connection.
The issue? I was using the windows note (Win+v) to paste the connstring since the beginning and in the string there is a / instead of \ in the instance name. I'm writing here to not smash everything...