// Mouse Down won't register
void DrawMyWindow (int windowID) {
	// code
	if (Input.GetMouseButtonDown(0)) {
		Debug.Log ("MOUSE DOWN!");
	}

	if (Input.GetMouseButtonUp (0)) {
		Debug.Log ("MOUSE UP!");
	//	more code
	}
}

// Mouse Down works fine
void Update () {
	if (Input.GetMouseButtonDown(0)) {
		print ("Mouse Button Down !");
	}
}