Check the BIOS to see if the motherboard can see the drives. If it can´t it is almost certainly either a cable fault. (I would have added a BIOS or battery fault, but that would have lost the HDD as well). If so, the two drives will probably be on the same cable. Reseat or replace.
If the BIOS can see the drives, but Windows cannot, it is a Windows fault. This is more difficult. There is no way to force Windows to see an IDE drive. They can vanish because of viruses, bad drivers, protection software such as Sony´s root kit. To be honest, if it is Windows, it usually ends up easier to reformat and reinstall the OS