Iomega 250 zip disks are no longer readable

Recently I had to restore my PC to out-of-the-box condition. I moved many files onto ZIP discs in order to preserve them! The zip drive itself is external to the machine and seems to work fine. However, it has stopped reading two of the zip disks on which I have files.

The first disk contains my IE bookmarks. There is a folder called Favorites. when I insert this zip, the autoplay comes up and eventually opens the disk to display the Favorites folder. When I click on the folder, I get an error message that the disk is not accessible. I cannot read this disk on anyone's PC... I've tried. It won't let me save anything to it either nor can I use disk clean-up or disk defragmenter. Using Properties, it appears there is info on the disk. I cannot access the info, however.

The second zip disk contains (or used to) about 300 MS Word files that I wanted to preserve. I accidentally left the disk in the zip drive during a reboot. I can no longer see the contents of the disk and it acts similarly to the first disk described above.

Any thoughts on how I might recover my files from these disks?

I'm running Windows XP with SP2 up-to-date.

 

*bump*