Hi, After I installed a new hard drive I updated it with Mavericks. I had a thumb drive which I used to back up info from old hard drive. I had it in one of the USB ports and everything worked well for weeks. I was busy doing other things and never put the data from the thumb drive on my new hard drive. I used the thumb drive a couple of times to look at some documents, so I know it worked with the new setup. Yesterday, I tried to access the thumb drive and it was showing on my desk top. I rebooted, received a massage saying, it dosent recognize the thumb drive anymore would i like to initialize, ignore or eject. I can't get the iMac to recognize my thumb drive anywhere. I tried using the thumb drive on a PC and it also asked if I would like to format the thumb drive. Not working on PC either. I tried a different thumb on my Mac and it worked. My problem is that I need the data on the thumb thats not working anymore. Any Ideas on why this happened and how I can retrieve the data from the thumb drive when my mack won't recognize it. Again, other thumb drives do work and the thumb that failed worked at one point also. Help Please!!! Thx Tony