Script Errors when nothing wrong...I think

Ok, I am a beginner, so it could likely be somet$$anonymous$$ng I'm doing wrong, but I don't t$$anonymous$$nk so. I put the below script in Unity before and it worked, but now as I was editing stuff at the bottom (the About Game guiMode and the How to Play guiMode), it gave me these errors:

(17, 20 [ if(guiMode = "Main") ] ) - BCE0044: expecting ), found '=').

(17 22) - BCE0043: Unexpected token: Main.

(20, 17 [ just under //New Game Button ] ) - BCD0043: Unexpected token: if.

(20, 119) UCE0001: ';' expected. Insert a semicolon at the end.

(22, 61 [ PlayerPrefs.GetInt......] ) BCE0044: expecting :, found ';'.

 #pragma strict
 @script ExecuteInEditMode()
 
 var myGUI : GUISkin;
 var buttonWidth : float;
 var guiMode : string = "Main";
 
 function Start()
 {
     guiMode = "Main";
 }
 
 function OnGUI()
 {
     GUI.skin = myGUI;
     
     if(guiMode = "Main")
     {
         // New Game
         if(GUI.Button(Rect (Screen.width/2-(buttonWidth/2), Screen.height/2-20, buttonWidth, 30), "New Game"))
         {
             PlayerPrefs.GetInt("playerLevel", 1);
             Debug.Log("New Game Clicked");
             Application.LoadLevel(1);
         }
         
         // Continue Game
         if(PlayerPrefs.HasKey("playerLevel"))
         {
             if(GUI.Button(Rect (Screen.width/2-(buttonWidth/2), Screen.height/2+20, buttonWidth, 30), "Continue Game"))
             {
                 Application.LoadLevel(PlayerPrefs.GetInt("playerLevel"));
             }
         }
         else
         {
             GUI.Box(Rect (Screen.width/2-(buttonWidth/2), Screen.height/2+20, buttonWidth, 30), "Continue Game");
         }
         
         //How to Play
         if(GUI.Button(Rect (Screen.width/2-(buttonWidth/2), Screen.height/2+60, buttonWidth, 30), "How to Play"))
         {
             guiMode = "HowTo";
         }
         
         //About Game
         if(GUI.Button(Rect (Screen.width/2-(buttonWidth/2), Screen.height/2+100, buttonWidth, 30), "About Game"))
         {
             guiMode = "About";
         }
     }
     
     if(guiMode = "HowTo")
     {
         Debug.Log("How to Play");
     
         //Back to Main Menu 
         if(GUI.Button(Rect (Screen.width/2-(buttonWidth/2), Screen.height/2+100, buttonWidth, 30), "About Game"))
         {
             Debug.Log("About Clicked");
         }
     }
     
     if(guiMode = "About")
     {
         Debug.Log("About Game");
         
         //Back to Main Menu 
         if(GUI.Button(Rect (Screen.width/2-(buttonWidth/2), Screen.height/2+100, buttonWidth, 30), "About Game"))
         {
             Debug.Log("About Clicked");
         }
     }
 }

What am I doing wrong?