^^ yeah, it appears it is not the HDD or its cables - in fact, your story says even an IDE drive could not work! Certainly focuses on the mobo.
If you want to check further just to be sure, get from WD's website their Data Lifegard utility in a form you can burn to a CD or floppy that is bootable directly. Then you don't need Windows to run. Run its tests on the HDD and see what they say. It might show a bad HDD (two of them in a row??), or it might show you more clearly what IS wrong.