Try an OS repair from the OSCD.
Nogo? Try an operating system re-installation.
Neither go? Try switching the Drive port on the motherboard. I tell u this cuz it seems that it'll intermittently recognize the HDD.
Nogo? Try a different HDD. Whatever the outcome is, let us know, & whatever it happens to your pc's or however they are doing performance-wise, do back up on a regular basis.