C# how to stop execution until message box button is clicked

See more:

C#

My program catches event msg from my .dll.
It then shows the MessageBox. Then exit the program.
However, you can ignore the MessageBox button and continue to use the program.
So I want to disable the program until I press the OK button.
I would like to disable the program.

What I have tried:

private void ExitProgram(object sender, EventArgs e)
        {
            string msg = sender as string;
            Log.Instance.InsertLogError(msg);

            DateTime nowTime = DateTime.Now;

            while (Log.Instance.GetLogQueueCount() != 0 || nowTime.AddSeconds(10) < DateTime.Now)
            {
                Thread.Sleep(100);
            }
            Log.Instance.Dispose();

            MyProgramtWindowsModeErr(msg);
            //if (Program.bWindowMode == true)
            //    MessageBox.Show(msg, "MyProgram", MessageBoxButtons.OK, MessageBoxIcon.Error);

            (Process.GetCurrentProcess()).Kill();
        }


        public bool MyProgramtWindowsModeErr(string msg)
        {
            if (Program.bWindowMode == true)
            {
                MessageBox.Show(msg, "MyProgram", MessageBoxButtons.OK, MessageBoxIcon.Error);
                return false;
            }
            return true;
        }

In MyProgramtWindowsModeErr, I checked true and fasle for each other.

However, I could not open the message box or continue using the program.
Help me plz..