mouse enter Click problem

hey guys i have a problem my little program wil not work

here is the script

 function OnMouseEnter(){
 if (Input.GetButtonDown ("Fire1")) {
      Application.LoadLevel ("SGC");
     }
 }

it should work right?

its for my main menu play button witch is a gui text but i want to change it to a litle plane in front of the camera with a texture that i have it says play and im gonna add a box collider on it. and i also gave the gui text a box collider but my textures are better than the fonts from unity so that way i wanted to do it with a plane and texture. i got it all reddy but the script wont load the level SGC and i have added it on the build settings. i have triad this it works it loads the level when i hover over the play buton but i want to be able to first click it than load

 function OnMouseEnter(){
 Application.LoadLevel ("SGC");
 }