A lot of times you will have to change the boot order to boot from a USB flash drive. Try connecting the USB flash drive and booting into the BIOS, then change it so your flash drive boots before the HDDs.
I have the same mobo... and yes it does support usb booting.
As MrYoink said, you'll have to select the flash drive as the first boot device or there's an option where you can boot from the flash drive without messing with the bios. (Its some Fn key to select boot device F12 i think but not sure...)