Mounting USB Iomega ZIP250

[achana saysit com]

Hi!
I have been working with the USB drive on Redhat 7.1 (2.4.2-2) for a
year and I am happy with it until this morning.
I disconnected it and used it on a laptop (W98). In the meantime the
Linux box was rebooted.
When I plugged the USB Iomega into linux again, and tried mounting it
with :
# mount -t -vfat /dev/sdc4 /mnt/zip250 
it gave me a "not valid block device" error message.
I then looked at fstab and found that after the reboot without the USB
drive, the entry was gone !?!  I replaced the line , but got the same
error message. 
Can anyone help , shed light ?
THX

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