I have an Iomega portable hard drive. It doesn't seem to be working anymore. I noticed when I open the backup files that the last backup was 6/22/2014. Time Machine is up to date. I had a new drive installed in my Mac mini on 5/5/2014 because my drive failed. I also upgraded to Mavericks. I can see the backup icon moving and the external drive is blinking at times, but I don't see any updates. What could be the problem?