I have had a problem like this before. Plugging in the flash drive would work for a moment and then the drive would disappear. The cause in my case was a drive letter conflict. it seemed that the SD card reader was attempting to use the same drive letter for the removable SD card slot. I had to go into computer manager. Right click on my computer -> select manage then go to disk administrator. Here you can give the removable storage a different drive letter and this should resolve the conflict.