With the flash drive mounted run this as root:
# fdisk -l
that will list all partitions that the system recognizes, whether mounted or not. You should see one for your flash drive, usually /dev/sda if you don't have any sata or scsi hard drives. Next, unmount the flash drive and rerun, fdisk -l. You should still see the entry for your flash drive. To reformat the flash drive to ext2, run:
# mkfs -t ext2 /dev/sdax
where 'x' corresponds to the partition number on the flash drive(usually sda1).