Old hard drive no longer recognized after installing new one?

Pertinent specs:

OS - Windows 7 Home Premium 64-Bit (6.1, Build 7601)

MOBO Model - P67A-UD7-B3

Old HD Model - 9SL154-303

New SSD Model - MZ-7TE250

Hey all and thanks for checking my problem out. So I recently purchased a Samsung 250GB SSD and used the software that came with it to migrate my files and OS over to it. Luckily I had just cleaned up the old 1TB drive so I was just barely able to fit all the data I wanted to on it. Now I'd like to expand my storage space with the old hard drive but I can't seem to get the computer to recognize that it is connected.

Currently the SSD is working great ("omg its so fast i can die"). Some things that I've tried thus far is using the boot menu to see if I can still boot from the second drive and looking up the disk in Computer Management. Both of these checks did not show the old hard drive, only the SSD as my C: drive. One curious thing, though, is that the old hard drive will still be hot if I take it out of the case after shutting down, almost as if it was being used. Quite perplexing.

The only thing I can think of left to try is to reformat the old drive, but I have no idea how to do so if the OS and mobo both won't recognize that it is connected. I'm really at a loss here so any and all help is appreciated. Thanks in advance!