Hi DNJ
Amazing the difference a small bit of extra information makes.
The original discs were probably formatted in NTFS and when you loaded them into the Tyros it tried to format them in FAT 32, thus corrupting the partition.
Just connect them to your PC, go to disk management (As I previously mentioned) and delete the unrecognised partition, then create a new one, they will the show up in My Computer allowing you to format them as you wish.
Hope this helps

Bill