Visual Studio doesn't compile? A remedy

Strangely enough, Visual Studio did not compile my own project. The locked folder was 'obj'. I looked for the cause in various ways, but nothing. Then I understood:
The problem occurs when the program is already running on your computer before compiling.
So you have to do this:

1. Right click on the taskbar, at the bottom of screen
2. Click on 'Task Manager'
3. Among the processes select the one related to your project and click on 'End Task'

 Hello  everybody