Thank you @Matteov2.0 and @OfficerChris1 for your response. I've reset all my game data and installed GTA V again. (So RAGE is gone aswell, and (Now I have to start over again, but I don't care.))
I think the problem was in one of my Rockstar profile files. One was corrupted. So, now I can play again.
But I don't want to have the same problem again? So, how do I install LSPDFR scripts / mods the correct way?