Any changes I make to my code aren't doing anything. I've even tried putting lines in that I know will crash my program, and nothing. It just keep running the old version. It's even loading old versions of files I've edited and saved.
There a 3 projects in my solution. 2 are pure C#. 1 is a WinForms application.
It sometimes happens that some files "are being used by another process".
Close your solution and delete all "bin" and "obj" subfolders of all your projects that are included in the solution.
Then open your solution again, execute "Clean solution" and build it again.