I've actually had this problem on two separate occasions with what seemed to be the same issue. However, one was recoverable, the other wasn't. To find out if it's recoverable, download & install the trial version of an application called 'Data Recovery Wizard v4.3.6'. Run the wizard & click 'Complete Recovery', if it sees your flash drive then you are in luck. However, the trial version won't complete the recovery until you buy the Pro version. At this point do a web search for a similar free product until you find one that will recover it. Or you can spend the money for the Pro version. This was the only product that actually worked for me though. Good luck.