利用线程关闭已开启的应用程序，代码如下：

        using System.Diagnostics;

        public void CloseSoundApp()
        {
            Process[] pProcess;
            pProcess = Process.GetProcesses();
            for (int i = 1; i <= pProcess.Length - 1; i++)
            {
                if (pProcess[i].ProcessName == "应用程序名。如QQ")
                {
                    pProcess[i].Kill();
                    break;
                }
            }
        }