A Problem With A Script Of GUI.HorizontalSlider It Do not Move?

I'm Working On A GUI.HorizontalSlider For A Volumen Menu In My Game But I Don't Know Why When I Try To Scroll It For The Sides It Don't Move. I Think Is A Problem With My Script But The MonoDevelop Don't Show Any Problem Of Write Or Code This Is The Script:

 var ventana :Rect =Rect(20,20,100,50);
 var texmenu :GUISkin;
 var sfxVol : int = 6;
 var musicVol : int = 6;
 
 
 function OnGUI()
 {
 GUI.skin =texmenu;
 ventana =GUI.Window(0,ventana,ventanamenu,"Options");
         GUI.Label (Rect (550,114,100,50), "SFX Volumen");
         GUI.Label (Rect (550,214,100,50), "Music Volumen");
 }
 
 function ventanamenu(ventanaID :int)
 {
 
 if (GUI.Button(Rect(150,300,100,50),"Return"))
 {
 Application.LoadLevel("Menu");
 }
 
 if (GUI.HorizontalSlider (Rect (150,100,100,50), sfxVol, 0.0, 10.0))
 {
 sfxVol == GUI.HorizontalSlider; 
 
 }
 if (GUI.HorizontalSlider (Rect (150,200,100,50), musicVol, 0.0, 10.0))
 {
 musicVol == GUI.HorizontalSlider;
 
 
 }
 
 }