Hi,
which BIOS version are you running?
The latest official release for your motherboard is F6 available here:
http://www.gigabyte.com/products/product-page.aspx?pid=5478#biosor there is a newer beta BIOS over at TweakTown, F7a which you can download from here:
http://forums.tweaktown.com/gigabyte/28441-gigabyte-latest-beta-bios.htmlIf I were in your position I would update to the latest BIOS version if you haven't already done so.
In BIOS have you checked that the SATA ports are enabled?
Check under BIOS features that the all SATA support, is enabled.
Under the BIOS Peripherals page/SATA Configuration, check to see that the SATA ports are enabled. They should be enabled by default but it is worthwhile checking.
Stupid question but, have you made sure the SATA leads and power cables are connected properly at both ends? I had an issue once, with a modular PSU where the HDD power lead hadn't been plugged into the PSU properly and it took me ages to trace where things were going wrong.