Diver/K7T266 PRO (MS-680) MSI Socket A VIA VT8366 motherboard

If these units are pata ( parallel ATA) units, make sure they are set as masters or slaves which do not conflict with any other items on the same bus or cable.
If you have the hard drive on the same bus, make sure it is set to master and the optical drive is set to slave.
If these are SATA units, try swapping them onto another drive bus.
If this fails, have the units checked on another PC. This will confirm that the units are good and working, if they are not detected on another PC, then they may be faulty.
If you are using Windows 7, check for an updated driver and install it as W7 has a habit of ignoring older peripherals.