Asus P8Z68-V PRO/GEN3 Not detecting my hard drive

Hello,

Right now I'm getting very frustrated because it was working in the past, but my PC will always give me the same crap. "Reboot or insert boot drive" (Something like that, it's the message that any PC gives you when you first need to install windows.) I've already installed windows but it just won't do anything, and I've checked the BIOS under Advanced - Sata Config. and it says that none of my sata cables are plugged in. I've checked my sata cable connecting to my hard drive, replugged it back in, cleaned it, and plugged it in different slots and still I'm getting nothing. Any help would be appreciated.

My specs:
Intel i5 2500k
P8Z68-V PRO/GEN3
Asus Radeon 6870 HD
Corsair Vengeance 8 GB (2x4GB) 1600 mHz DDR3
Seagate Barracuda 7200 RPM 2TB SATA 6GB/s 64MB Cache