Ford Sync/Win 7 & Fat32 drive question

I have a new Ford that has the Ford Sync. I've had trouble finding something to work with Ford Sync from all kinds of usb thumbdrives, to Zune, to portable usb drive. I want it to show the artist/song title on the screen and be able to use voice commands to play songs/artists, etc. The only thing I could get to work was a USB portable Seagate 500GB portable hard drive. Solely powered by USB. It is the only thing that has worked properly in the Ford. I had to format it with Fat32 Format program before Ford Sync would recognize it. It formatted it to FAT32 and both my XP and Win 7 computers recognized it. I even put lots of media on it a few different times in the last week.
It still works with the Ford just fine but I wanted to add some of my new cd's to the hard drive and all of a sudden neither the XP or the Win 7 recognize it. It comes up as a drive in "My Computer" and "Computer Management" >"Storage" but if I try to access it, it gives me a screen saying it needs to format the drive. Which I don't want to do and lose my mp3's on there.
Why can you no longer see the drive? Did I do something wrong (although I would have no idea what. I only plug and unplug it into the Ford USB port and then into my computer to add songs). Is there anyway to correct this without having to reformat? I don't want to lose the files on the drive as it took time to tag them correctly so Ford would read them correctly.
Thanks for your help.
P.S. I have a blank hard drive from an old laptop 160GB that I also used the FAT32 Format program on but it won't show up a a drive period. I know it is getting power as the lights come on but nothing more. Any thoughts on this?

This website is not affiliated, owned, or endorsed by Microsoft Corporation. It is a member of the Microsoft Partner Program.