Just checking the C300 should be running off the GSATA3_6 port, and you need to install the Marvell Console Driver (SATA3).
First, for now, in the BIOS choose "Load Optimized" Save & Exit. The HDDs / DVD more than likely is causing the issue; your C300 is not running off the Intel chipset, but instead the Marvell GSATA3_6 - GSATA3_7.
Next, install ALL of the drivers listed - http://www.gigabyte.us/products/product-page.aspx?pid=3234#dl
Last, tweak the BIOS.