My Nook won't show up on my ADE; it was there last time, but now it's not. Any suggestions on what I can do to get it to show up, so I can put my library book on it?

                                                                                                                                                 My Nook won't show up on my ADE; it was there last time, but now it's not. Any suggestions on what I can do to get it to show up, so I can put                                                                  My Nook won't show up on my ADE; it was there last time, but now it's not. Any suggestions on what I can do to get it to show up, so I can put my library book on it?