If you have any files stored on them at the moment, back them up somewhere else for the time being. You will need to do this on XP as it won't recognize the drive at all in Vista. Plug the usb drive in and go to my computer, right click the flash drive and go to format. Once the format window appears, click start. When it finishes formatting the usb drive take it out and try it on Vista. A lot of other people had this problem and usually this fix works.