Does your motherboard POST screen have options like these? I also have a Gigabyte Motherboard
Press F2 for Setup
Press F11 for Boot menu
Or anything along the lines of "Boot Device" or "Boot Sequence". In my case I repeatedly press F11 while the computer is booting. Then it will show me a list of devices where I can choose to boot like:
Sometimes it could be like this:
USB-HDD: SANDISKCRUZER COLORS
The Sandisk Cruzer Colors is my flash drive. I hope there is a similar option in your computer just like mine. You don't need to enter the BIOS to set the boot priority. You just have to press the "Choose Boot Menu" key
"I learned a lot from repeatedly breaking my system and then reinstalling. Oh, and a lot of GOOGLE searches too!"