I have the same problem. I run two HDD. I reinstalled the system (XP) and applications on the system disk. when this was finished, the data hdd could not be seen by Windows explorer, or when using any application to open a file. Computer management can see the disk, including the origional name, but the right click commands are all greyed out except Delete Partition and Help. The disk assignment letter is missing. I have tried the disk in another machine but it is also not recognised.
does anyone have any ideas?