I have always been executing git-bash by clicking the "Terminal" button from Source Tree. It stopped working very recently: Clicking that button doesn't have any response. I navigated to the folder .../git_local and double clicked on the git-bash.exe. Nothing happens. No error message either. I also tried to execute it from command line, and again nothing.
I am on Windows 7 and I have admin rights.
Update: the problem is solved. There is a security patch that blocks mitty. IT white-listed it, then it works.