My girlfriend have 32gb Kingston USB harddrive which suddenly decided not to be visible on any computer any more. I used it to transfer pictures to her from my mac onto her computer running Windows Vista - no problem. She connects it to her fathers new Windows 8 computer - no problem, but when she connected it to her brothers Windows computer it (supposedly) mentioned something about "formatting hard drive" and "FAT32".

I've encountered same problem with my external Sata hdd, but it is still visible on my Macpro though. Therefore i thought my girlfriends USB drive would work on my mac again, so that we could empty it. But it's not visible.

What can I do to save the data before formatting it and what can I do to prevent it in the future?