Baked Alaskan: You could try right click on My Computer, and choose "Manage"

On the left side, under Storage, choose "Disk Management"

Then in bottom right, you should see all the drives connected to the PC - and should be able to right click on the un-mapped hard drive, and choose to assign a drive letter.

If it is not there - I guess the next thing I would do is manually disconnect the slave drive - boot up PC, then shut down - and then install the slave drive again to see if the PC will auto-find it.