The original Kindle Fire installs and shows as an external USB drive with a drive letter. I presume that is what you have.
Sounds as if you have just been unplugging the usb and have not rightclicked on the drive letter and 'ejected' the drive safely before you unplugged.
Can you confirm that that is what has happened? and you have the original Kindle Fire model and not the new HD one (as that will show as a media device)