I have an issue. I have been using a Seagate external hard drive on my macbook air to backup time machine. I went to back it up today like I usually do and no matter what I do my mac is not reading my Seagate! Every other time, I plug it in and it shows up. What do I do? I need to free up space because I don't have room to even back up my iPhone at this point. I think I did an IOS update last week...did that do something?