Not sure whether your computer's Gigabyte-brand motherboard uses BIOS or UEFI? Here's a quick guide to differentiating between the two: the interface of BIOS is usually monochrome and entirely text-based. Meanwhile, the interface of UEFI usually has pictures, and allows you to use your mouse pointer. If your Gigabyte motherboard uses UEFI, check out our UEFI settings guide instead.
To enter the BIOS on my own computer's Gigabyte P67A-D3-B3 motherboard, I have to press the delete key when it boots (before the operating system starts). Different manufacturers set different keys for opening the BIOS.
If your Hackintosh doesn't have any version of Mac OS X installed yet, you have to change a few extra BIOS settings. Before starting, reset all of your BIOS settings to their factory defaults. On Gigabyte motherboards, you can reset your BIOS settings to their default by selecting "Load Optimized Defaults" on the main page of the BIOS. Once your BIOS is running on its defaults, you need to change these three settings:
Boot Device - Change the boot device of your computer so that "USB-HDD" is first. You need to do this for Unibeast to work. After you finish installing Mac OS X, you should change this setting back to default, so that "Hard Disk" is the first boot device (this optional, but it will speed up your boot times).