I want execute .exe file on IIS server through ASP web page btnClick, im using Server.MapPath

It is impossible to call another UI application by the application hosted in IIS. Due to the fact that there is no user session to render the UI. Since Windows Vista, there is a mechanic called Session Isolation, which separates the application and the service. However, it will work when we start the application by Visual Studio locally since the current session is inherited with the account running Visual Studio.
For details, please refer to the below links.
How to start a process from an IIS hosted WCF service?
IIS Session isolation problem
 

try this code and see if you get any error. if you get an error check whether the published code bin has the HelloApp.exe.

protected void Button1_Click(object sender, EventArgs e)
    {
        string fileNameWithPath = Path.GetFullPath(@"~\bin\HelloApp.exe");
        ProcessStartInfo startInfo = new ProcessStartInfo();
        startInfo.Arguments = "";
        startInfo.CreateNoWindow = true;
        startInfo.UseShellExecute = true;

        startInfo.FileName = fileNameWithPath;

            using (Process exeProcess = Process.Start(startInfo))
            {
                exeProcess.WaitForExit();
                StreamReader outputReader = exeProcess.StandardOutput;
                StreamReader errorReader = exeProcess.StandardError;
                string errors = errorReader.ReadToEnd();
                if (!string.IsNullOrEmpty(errors))
                    throw new Exception(errors);
            }

    }