Have a look at it in GParted (which you might have to install first). It'll tell you if something's screwy with the partitions.
EDIT:
If so, the situation isn't good. You can use dd
to make a backup in case you figure out a way to recover the data, changing sdx
to the correct device and the of=
filename to your desired backup image name:
dd if=/dev/sdx of=/output/file.img
Basically, though, your partition table is probably corrupted. The only thing I know to do, absent some specialized tools which may or may not exist, is to delete the partition table and create a new partition(s). Of course, doing this will completely erase your flash drive; hence the backup I mentioned above.