new hard drive old slave drive not recognized

I recently had to install a new master hd on my laptop. My slave drive is in a removable modular bay. I removed it when I formatted my new master drive. when I have my removable hard drive in now with the new master it is not recognized. How can I get my old slave drive recognized without losing the info on the slave hd. the computer detects the slave drive as being there, but does not assign it a drive letter.