Hard Drives Not Detected

[TranquilRed]

So my friend's machine, which I built and am thus responsible for, started acting up a while ago, after installing Oblivion he says. It would boot to an error message which was remedied with a little Repair Console. After getting it to boot to desktop, where everything works flawlessly, I decided to restart it. On restart, it didn't detect either hard drive. I swapped the SATA cables, unplugged one and not the other, etc. Absolutely nothing, the BIOS pretends like there isn't a single hard drive connected. Installing Windows behaves similarly, it just pretends there is no drive connected. What is the problem here?

 

[Nenu]

Have you tried resetting the CMOS?
Are the drives recognised in another PC?