cannot access the next scene

firstly, the scene will be loaded to the TPS4 scene after the user click on the text from mainmenu scene...after the user done with the game, a new scene(win scene) will appear which is ask the user if the user want to play again or exit to desktop...when the user hit play again, the mainmenu scene is loaded...I tried to access mainmenu scene after the user chose play again. when the mainmenu scene appear, the user will click on the text which is loaded to the mainmenu scene again..however, it doesn't loaded..just stuck in the mainmenu scene

anyone can fix it??

this is my code for mainmenu scene

 var soundhover : AudioClip;
 var beep : AudioClip;
 var QuitButton : boolean = false;
 function OnMouseEnter(){
     audio.PlayOneShot(soundhover);
 }
 function OnMouseUp(){
     audio.PlayOneShot(beep);
     yield new WaitForSeconds(0.35);
     if(QuitButton){
         Application.Quit();
     }
     else{
         Application.LoadLevel("TPS4");
     }
 }

and this is my code for win scene

     var buttonHeight:float=500;
     var buttonWidth:float=500;
     var buttonSpace:float=50;
     var titleTexture:Texture2D;
     var customSkin:GUISkin;
     var customStyle:GUIStyle;
     
         function OnGUI(){
             GUI.skin = customSkin;
             GUILayout.BeginArea(Rect(Screen.width/2-buttonWidth/2,Screen.height/2-buttonHeight/2,buttonHeig
 
 ht,buttonWidth),customStyle);
         GUILayout.Space(50);
         GUILayout.Label(titleTexture);
         GUILayout.Space(buttonSpace);
         //GUILayout.Box("Please Select");
         if(GUILayout.Button("Play Again")){
             Application.LoadLevel("mainmenu");
         }
         GUILayout.Space(buttonSpace);
         if(GUILayout.Button("Exit to Desktop")){
             Application.Quit();
         }
         GUILayout.Space(buttonSpace);
         GUILayout.EndArea();
     }