Well, here's some updates of my martyrdom trying to log in!
Today I reinstalled the NClauncher after a lot of tries to log in. And I tried a couple of times with the reinstalled launcher, but nothing. So I decided to restart the PC, and it worked. I played for about 3 hours, but I had to restart the PC again and guess what? I can't log in again! See, it's random when I finally manage to log in.
The problem isn't my connection or with my PC, it's something NCfail is doing or not doing.