Garage Band Noise Gate Question. How to turn ON?

Hello, I just installed Garage Band and I am using input 1 and for recording a vocal. There are some background noises so I wanted to delete that. So I went online and found out about Noise Gate. But, somehow on my computer the Noise Gate level and turn on button is faded out and when you click on it notting happens, its just keeps being faded out and unable to be turned on. Is there any specific reason why that happens??? Any solutions ??? PLEASE HELP !

Thank you