They may be formatted as CDFS
how to remove the CDFS partition & reformat it.
Download this click here,
do a virus scan then run umptool2090.exe, click "settings", tick "need format"
then click the button 2nd from the right at the bottom of the form (the form isn't sized properly as I could only see the top few pixels of the buttons so just tab until you get the correct button).
The settings form will close and the scan mode will show as "high level scan format".
Click the button that displays the drive letter & you should now have a clean drive with 1 partition.