Did you try changing jumper settings so one HD is the master and 2nd is the slave. Also, try leaving only the problem HD connected, and check that the system recognizes it correctly. If so, then jumper settings are definitely at fault. Also, your IDE data cable <should> support cable select, but not all IDE cables are correctly to support that function. That's why I asked about the Master/slave jumpers. If you're not sure about which positions to 'jump', go to the manuf web site, they usually have clear info about complete jumper settings for all HD models (make sure you look at your specific model) LOL
Serendipity is a lucky guess !