your pendrive is damage or may be the partition is deleted or format is changed. conect your pendrive then right click on my computer then manage then disk manager. then just right click on your pan drive at there and see what option is available. use format or partion it. hope it will help you out. if problem presist open your pen drive and take a little bit petrol/ip water and brush and clean it after a few min again connect the pendrive to pc an see if it start or not. if not then buy new pen drive.