The slave cord and the master have to be plugged in right, for instance if you plug a slave in to the slot but do not enable in your Bios(?) then it might not show up. At least that is what I have experienced in the past.
I'd check the drives for a slave/master issue then. Try this tutorial out to see if you can get it working http://www.mikeshardware.com/howtos/howto_connect_ide_hd.html
Got it. I had the Slave/Master jumpers connected improperly. Thanks