I have hard drive issues with my sabertooth x79 also ... asus tech support was no help. I'm trying a few things right now and will let you know what I find that works. Hopefully it will help you out too.
Yes as I stated before, I have the x79 and ran into hard drive issues. This was cured with a bios update. I believe this will help you. The others that posted are definately on the right track.
our problems were a bit different but with similarities. here is the like to my thread that would be marked solved soon.