IENumerator does not work

Hi, I'm still new with c# and still learning, thats why I'm stuck around here.

What I'm trying todo is.. making the gameobject and entire script to pause and then continue after 2 seconds.

Many had put up a discussion about this, but I can't seem to get the code right.

I searched alot on the internet, and decided to use yield waitforseconds and then call using startcoroutine into my void function. But, I really don't know what I did wrong. There is no error in code, and none effect on my program too...

This is the part of the codes :

 public void CheckAnswer()
     {
         string userAnswer;
         userAnswer = inputField.text.ToUpper ();
         if (userAnswer == answer) {
             Debug.Log ("correct");
             AudioIsPlaying.isPlayingWrongCorrect = 1;
             ++MyScore.score;
             ++MyScore.stage;
             if(MyScore.stage == 2){
                 Application.LoadLevel ("main2"); 
             }else{
                 Application.LoadLevel ("main");
             }
         } else {
             Debug.Log ("Wrong");
             AudioIsPlaying.isPlayingWrongCorrect = 2;
             if(MyScore.live == 1){
                 MyScore.score = 0;
                 MyScore.stage = 1;
                 Application.LoadLevel ("GameOver"); //go to gameOver Scene
             }else{
                 --MyScore.live;
                 txtLives.text = MyScore.live.ToString ();
             
                 StartCoroutine(WaitPopup(5)); // I can't get this work
 
                 Application.LoadLevel ("main");
             }
         }
     }
 
     IEnumerator WaitPopup (float duration){
         Debug.Log ("test1"); 
         popupwrong.SetActive (true); // the game object I wanted to show and then pause
         Debug.Log ("test2");
         yield return new WaitForSeconds (duration);
         Debug.Log ("test3");
         popupwrong.SetActive (false);
     }

Thank you