Does your BIOS have a "add to boot list" option? On my last build i had to go in and select different items to add to the boot list before i could select them. Also, what format is your USB drive, and is the OS file in .iso format?
I formatted the usb in fat32, yes it is a iso image downloaded from the ubuntu official site with unetbootin, I did utilize the same usb in the past and it did work well... are you in knowing of a method to fix the eventual bios errors/ to fix the fact of not detecting the usb?
Thank you for your answers!