// Get a handle to an application window.
        [DllImport("USER32.DLL", CharSet = CharSet.Unicode)]
        public static extern IntPtr FindWindow(string lpClassName,
            string lpWindowName);

        // Activate an application window.
        [DllImport("USER32.DLL")]
        public static extern bool SetForegroundWindow(IntPtr hWnd);
...............

            Process process = new Process();

            //process.StartInfo.FileName = @"CALC.EXE";
            process.StartInfo.WorkingDirectory = @"D:\ED_13";
            process.StartInfo.FileName = @"HELIX.EXE";

            process.Start();

            MessageBox.Show("Continue?");
            IntPtr handle = process.MainWindowHandle;
            //IntPtr handleW = FindWindow("ConsoleWindowClass", @"D:\ED_13\HELIX.EXE");
            //IntPtr handleW = FindWindow("CalcFrame", @"Калькулятор");
            bool h;
            if (handle == IntPtr.Zero)
            {
                MessageBox.Show("Calculator from process is not running.");
                return;
            }
            else
                h = SetForegroundWindow(handle);

            SendKeys.SendWait("777");