|The Asus P4C800-E has an option to enable/disable the SATA integrated controller. In fact, there may be a setting in the BIOS software as well as the jumper on the motherboard.|
If either one of these has been disabled, the BIOS won't see the SATA drive(s).
If you reset the factory default on your motherboard, I'm pretty sure ASUS does not include SATA-enabled as part of the default.
Other possibilties are that the power lead which attaches to the SATA drive is not securely in place, or that the data cable (4 wire lead) has been detached at either the motherboard interface, or at the drive itself. Double check the cables, as they gave me a hard time the first time I tried to install a SATA drive. I was not blessed with ballerina fingers.
Cabling can really be a pain, especially if you're using lots of bays for your drives. Healthy ventilation requires that you leave space between the drives, but that's exactly the condition that can stretch the cables to their absolute limits.
Don't skimp on length:
Beauty of the high sierra,
and she's looking out for you.