This is a bizarre issue I am having. It started with my Messages Desktop APP not being able to send attachments (PDF, JPEG, PNG, etc) via the drag and drop method. I tried to trash some preferences, but now landed in a worse place. When I go to the preferences with the APP, I am missing several things including the A/V menu, etc. I cannot even get up my preferences for my account. Aside from reinstalling Yosemite, is there an easy solution to this?