New Hard Disk for Pentium II PC

I just purchased an 80GB Seagate ATA 100 drive for an old Pentium II PC. However, when I connect the hard disk to the computer and boot it up, the BIOS tries to recognise it but nothing happens. I have set the CMOS option for Primary Master disk to AUTO with LBA mode enabled. The jumpers are also set to Master on the hard disk.

It currently has 2 x 8GB hard disk and a CD ROM drive.

Do I need to upgrade the BIOS?
or Do I need to buy a PCI IDE Card to connect my new Hard disk? If I need a new PCI card, do I need one which is PCI 2.1 compliant or are they backward compatible as well?

Any help would be much appreciated.
Thanks