Windows 8 has secure boot technology. You should be familiar with the difference between Windows 7 and 8 BIOS settings, (Secure boot, fast boot, CSM Compatiblity Support Module, UEFI, legacy).
The manual for mobo revision 2 states:
OS Type
Allows you to select the operating system to be installed. Set this item to Windows 8 for Windows 8
operating system. (Default: Other OS)
This is the wrong default setting for you.
CSM Support
Enables or disables UEFI CSM (Compatibility Support Module) to support a legacy PC boot process.
Always Enables UEFI CSM. (Default)
Never Disables UEFI CSM and supports UEFI BIOS boot process only.
This item is configurable only when OS Type is set to Windows 8 or Windows 8 WHQL
Video card info: (Your video card probably has this and is set in the wrong position for Windows
Dual BIOS ( Legacy and UEFI ) Support
This product supports both Legacy and UEFI BIOS. By factory default, the card itself is under Legacy mode.
By pressing the button with SAPPHIRE logo, UEFI mode will be easily enabled.
CSM Support in the motherboard BIOS is really for Windows 7 or video cards that don't have UEFI support. However the choice is yours.
If using UEFI for Windows 8 I would set CSM to [Never].
Never Disables UEFI CSM and supports UEFI BIOS boot process only.
This item is configurable only when OS Type is set to Windows 8 or Windows 8 WHQL
You have a 500GB drive.
#1 to use UEFI you will be using GPT format. I think Windows 8 will set up the partitions for you.
#2 to use legacy, that will use the old MBR format.