Boolean flashing on and off

My boolean is turning true and then turning false rapidly and that results in a flashing menu. I’m trying to make it so you open and close a menu with the same key. I looked all over these forums to no avail. I’ve tried just about everything and I don’t know what I’m doing wrong.

	void Update()
	{
		if (Input.GetAxis ("OpenMenu") != 0) 
		{
				if (menuOpen) {
								menuOpen = false;
								inventoryOpen = false;
								cellphoneOpen = false;
						} else {
				menuOpen = true;
				inventoryOpen = false;
				cellphoneOpen = false;
						}
		}

Also, I would appreciate help with my other question that people refuse to answer because of how little sense it makes.
http://answers.unity3d.com/questions/691773/boolean-will-not-set-to-false-unless-i-minimize-an-2.html

As it is a button you should be using Input.GetButtonDown(“OpenMenu”) to solve the problem, this requires the user to release the mouse before it goes true a second time which should solve your problem.