JavaScript GUI.Window OverPowers GUI.Button

Hey guys, i'm creating a horror game, i have had a GUI Skin made for this game. I have one problem, when applying the skin, the GUI.Window covers over the GUI.Buttons, and moves the position of them, please help, here are my scripts.

 var mainMenuSceneName : String;
 var pauseMenuFont : Font;
 private var pauseEnabled = false;    
 var guiskin : GUISkin;        
 private var windowRect : Rect = Rect (Screen.width /2 - 100 ,Screen.height /2 - 100 ,250,200);
 
 function Start(){
     pauseEnabled = false;
     Time.timeScale = 1;
     AudioListener.volume = 1;
     Screen.showCursor = false;
 }
 
 function Update(){
 
     //check if pause button (escape key) is pressed
     if(Input.GetKeyDown("escape")){
     
         //check if game is already paused        
         if(pauseEnabled == true){
             //unpause the game
             pauseEnabled = false;
             Time.timeScale = 1;
             AudioListener.volume = 1;
             Screen.showCursor = false;    
             GetComponent(MouseLook).enabled = true;    
             Screen.lockCursor = true;
             
         }
         
         //else if game isn't paused, then pause it
         else if(pauseEnabled == false){
             pauseEnabled = true;
             AudioListener.volume = 0;
             Time.timeScale = 0;
             Screen.showCursor = true;
             GetComponent(MouseLook).enabled = false;
             Screen.lockCursor = false;
         }
     }
 }
 
 private var showGraphicsDropDown = false;
 
 function OnGUI(){
 
      GUI.skin = guiskin;
 
     if(pauseEnabled == true){
         
 
         
         //Make Main Menu button
         if(GUI.Button(Rect(Screen.width /2 - 100,Screen.height /2 - 50,250,50), "Main Menu")){
             Application.LoadLevel(mainMenuSceneName);
         }
         
         //Make Change Graphics Quality button
             if(GUI.Button(Rect(Screen.width /2 - 100,Screen.height /2 ,250,50), "Change Graphics Quality")){
             
             if(showGraphicsDropDown == false){
                 showGraphicsDropDown = true;
             }
             else{
                 showGraphicsDropDown = false;
             }
         }
                             //Make a background box
         GUI.Window(0, windowRect, OnGUI, "Main Menu");
         
         //Create the Graphics settings buttons, these won't show automatically, they will be called when
         //the user clicks on the "Change Graphics Quality" Button, and then dissapear when they click
         //on it again....
         if(showGraphicsDropDown == true){
             if(GUI.Button(Rect(Screen.width /2 + 150,Screen.height /2 ,250,50), "Fastest")){
                 QualitySettings.currentLevel = QualityLevel.Fastest;
             }
             if(GUI.Button(Rect(Screen.width /2 + 150,Screen.height /2 + 50,250,50), "Fast")){
                 QualitySettings.currentLevel = QualityLevel.Fast;
             }
             if(GUI.Button(Rect(Screen.width /2 + 150,Screen.height /2 + 100,250,50), "Simple")){
                 QualitySettings.currentLevel = QualityLevel.Simple;
             }
             if(GUI.Button(Rect(Screen.width /2 + 150,Screen.height /2 + 150,250,50), "Good")){
                 QualitySettings.currentLevel = QualityLevel.Good;
             }
             if(GUI.Button(Rect(Screen.width /2 + 150,Screen.height /2 + 200,250,50), "Beautiful")){
                 QualitySettings.currentLevel = QualityLevel.Beautiful;
             }
             if(GUI.Button(Rect(Screen.width /2 + 150,Screen.height /2 + 250,250,50), "Fantastic")){
                 QualitySettings.currentLevel = QualityLevel.Fantastic;
             }
             
             if(Input.GetKeyDown("escape")){
                 showGraphicsDropDown = false;
             }
         }
         
         //Make quit game button
         if (GUI.Button (Rect (Screen.width /2 - 100,Screen.height /2 + 50,250,50), "Quit Game")){
             Application.Quit();
         }
     }
 }




 #pragma strict
 
 var InventoryEnabled = false;
 private var windowRect : Rect = Rect (Screen.width /2 - 280 ,Screen.height /2 - 280 ,650,500);
 
 
 var InvWindow : Texture;
 var InvClose : Texture;
 var Grids : Texture[];
 var SideBar : Texture[];
 var guiskin : GUISkin;
 
 private var GridValue : float = -1;
 
 function Update(){
 
     
     if(Input.GetKeyDown("c")){
     
             
         if(InventoryEnabled == true){
             
             InventoryEnabled = false;
             Time.timeScale = 1;
             AudioListener.volume = 1;
             Screen.showCursor = false;    
             GetComponent(MouseLook).enabled = true;
                         
         }
         
         
         else if(InventoryEnabled == false){
             InventoryEnabled = true;
             AudioListener.volume = 0;
             Time.timeScale = 0;
             Screen.showCursor = true;
             GetComponent(MouseLook).enabled = false;
             
         }
     }
 }
 
 function OnGUI ()
 {
      GUI.skin = guiskin;
 
     if(InventoryEnabled == true)
     {
         GUI.Window(0, windowRect, OnGUI, "Inventory");
         
         //Grid
         GridValue = GUI.SelectionGrid(Rect(Screen.width / 2 - 280, Screen.height / 2 - 280, 500, 200), GridValue, Grids, 4);
 
         //Side Bars
         
         
     }