I would run a scan of the computer you have this plugged in to, and reformat the drive. Under 'My Computer' you should be able right click the drive and select format. This will erase EVERYTHING on the drive, however, so you'll want to save anything on there that you would want to keep. Sometimes, if the drive has been sitting around for a while, or if the drive was set up as a bootable flash drive, you may not be able to delete everything without reformatting.
Hope this helps.