2013 MacBook Air Sound Not Working

Please help! The sound on my MacBook Air is not working. When I try to manipulate the audio, a cross sign shows up and nothing comes out. When I checked the sound preferences, for some reason the audio is stuck on mute as shown in this picture. I have shut down and restarted the computer with and without headphones, but whenever I open it up, it shows the same thing in audio preferences. I have also tried clearing the headphone jack but nothing works and there is no red light that signals a problem. If you know what is going on, it would be really appreciated if you could help me. Thank you.