I recently had a similar problem, however mine was with a 2gb SD memory card..
I had only ever used that card in my Digital camera, but it would not read it any longer.
I tried multiple things, and what finally worked, was I stuck it in my Palm (Palm Treo 700) and for some reason it recognized it. I formatted it in the palm (FAT Only) then when I put it back in my card reader on the PC, I could format it for the FAT32, and all was well. I know this won’t help you much, as palm’s and PocketPC’s Don’t have USB Slots, but maybe it can help you find a work around…
If you can still see the drive, when you put it in the computer but just not open or delete the files, you can format it…
You run windows??
Justin