Audio Input problem

Hello and a good day to everyone. I'm having a problem with my macbook pro (2013 13-inch model). One day I was trying to use my Macbook as a speaker using my iPhone. I know this is kind of hard to understand but please bear with me. it's something like iPhone --- Audio Output---> Macbook and when I changed my settings in system preferences, it showed "unknown device" so I just clicked on it thinking that nothing would happen but then System Preferences started to freeze. I thought it was only for that moment but now whenever I try to change the input it will still freeze. I have no problems with output though it's just the input. I tried resetting the PRAM to no avail.