Hard drive lost drive letter

I recently formated my C drive and installed MS XP after my 60 gig drive said it was full. I moved all of my music, pics and other files that I didn’t want to loose on to a 40 gig back up slave drive. After the install I went to retrieve those file but was unable to see the back up drive. It shows in bios and storage management but not in my computer. It doesn’t have a drive letter assigned to it and in storage management drive letter assign option is grayed out. Any suggestions? I’ve tried to make it a master on its own channel but it is not recognized.