What does Disk Management show it as? All free space or partitioned?
My first guess is that your partition/format got corrupted and you will need to use some sort of free recovery tool if there is data on that flash that you need. If there isn't, you could reformat it, but I wouldn't trust my data to something that had already failed. I'd throw it into the nearest woodchipper.
This thread had some recovery tools, but more aimed at HDDS: http://www.tomshardware.com/forum/267620-32-best-data-recovery-tools
Look at the recovery links in this: http://www.tomshardware.com/forum/272402-32-flash-drive