I believe I may have had a similar issue, what is your MOBO? In the BIOS on my MOBO it shows the primary drive and only allowed me to select one drive and the optical, but I believe there is another spot to change which shows as the primary data drive and there I could toggle between my SSD and HDD, which then changed my option in the primary drive area. Just a suggestion, may not be the same issue.
I have an ASUS P8Z77-V pro and I think it actually is working now but it isn't showing in the main BIOS page under the boot priority, it's just showing my optical and ssd. However, under advanced settings it shows it under the SATA 3Gb/s slot.
I don't think it's an old HDD, it's a western digital caviar black 1.0 TB SATA II