[C#][WinForm]Prevent same process to be executed more than once at the same time: a simple approach

This is a simple and easy way to do it if your requirement is simple. Otherwise you should use Mutex.

using System.Diagnostics;

private void Form1_Load(object sender, EventArgs e)
{
    try
    {
        string strModuleName = Process.GetCurrentProcess().MainModule.ModuleName;
        string strProcessName = Path.GetFileNameWithoutExtension(strModuleName);
        Process[] aryProcess = Process.GetProcessesByName(strProcessName);

        if (aryProcess.Length > 1)
        {
            MessageBox.Show("This program is running already!");
            this.Close();
        }

        //...
    }
    catch (Exception ex)
    {
        //...
    }
}

Note: This will check the process based on the filename. It will not work if the filename is different. For example, if you make a copy of your program (let's say FindMP3.exe) and rename it to a different name like FindMP3_1.exe. That means, people can run FindMP3.exe and FindMP3_1.exe at the same time.

You can find other approaches from here.