USB HD no longer recognized

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I bought a new 80G Toshiba 2.5" HD to use as a backup USB drive for my
ancient desktop.
I run Win 98SE on the 233Mhz desktop.

At first the desktop couldn't see more than 10G of the USB drive.
Someone suggested updating the Fdisk to a newer version.
I did and bingo, it could now see 80G.

I partitioned the drive into 4 partitions and started transfering files
from the desktop to the USB drive. I did it a little bit at a time for
a few weeks. I must have transferred files for a total of three or four
sessions, with no problems.

Then today I plug in the USB drive and no go!
The desktop sees a USB drive, but it's only 10G again, and there is
nothing on the drive !!!!!

Someone please help me!
I didn't backup those files, I transferred them to clear out space on
my desktop HD.

Please tell me what I should try, ending as a very last resort with
Fdisk-ing the HD.

Thanks!

Ric