Hello,
I created a new Windows Forms .NET project. Then into the Form1 class in
Form1.H , I defined a public-signatured static Mutex object as below:
 ....
 public __gc class Form1 : public System::Windows::Forms::Form
{
  public: static System::Threading::Mutex *mt = NULL;
   ...
 }

Then, into the main function of application that starts the program, I coded
blow statements:

#include "stdafx.h"
#include "Form1.h"
using namespace RunOnlyOnceAtATime;

[System::STAThreadAttribute]
void __stdcall _tWinMain()
{   
 Form1::mt = new System::Threading::Mutex(false, "myMutex");
 if (!Form1::mt->WaitOne(10, true))
 {
     // Another copy of program is running
     MessageBox::Show(S"Program is already running.", S"Working Program");
     return;
  }
  else
  {
      //Run application.
      Form1::mt->WaitOne();//Yalnızca bu çalışıyor mutexi kilitliyelim
      Application::Run(new Form1());
   }
}

Above codes solved my problem. Thank you very much.