Answer: Try to press CTRL + ALT + DEL , and then select TASK MANAGER on the screen. A window will pop up, showing you all the programs that are being used at that moment. The one that isn't working is going to be shown as "NOT RESPONDING", and then you should just select it and click on "FINISH TASK", on the lower right corner. The program will be closed, then, and you can rerun it if you want.
