Problems with my Quaker Parrot?

He has been very aggressive lately and very noisey. I know that if they feel neglected that they will start to screech and become hostile but I try and pet him and play with him everyday, he allows me to feed him his bird seed but everytime I even get near his cage, which is in my room he lunges at me, practically hanging off his cage to bite me. When I bought him from the pet store in Spring last year, he was very cuddley and social. He would let me pick him up whenever and would interact with everyone in my family. I started noticing a change when little white things started appearing on the back of his neck. It looked like his feathers were encased in some type of film. I have no idea what it is.. He didn't have them when I bought him and the pet store owner told me he was about four years old. Could it possibly be any kind of molting? I am desperate to find something to make him the happy and social bird that he was. He has just become a pain lately. PLEASE PLEASE HELP!