|Is the hard drive an IDE type connection or a SATA type? If IDE you may have jumpers set incorrectly. Most Western Digital IDE drives have two Master jumper settings. One for Master alone, and one if there is another drive connected to the same cable. |
When using two drives on the same cable one must be set as master and the other as slave. Or, both must be set to CS.
The power or data cables may not be connected correctly or cables can go bad,
What is the full model number of the hard drive.
Watch the POST screens at start up to see if the drives are being properly by both model and FULL capacity.