You disabled secure boot, or you enabled legacy boot (which requires you to disable secure boot)? Windows 8 machines typically won't boot off USB by default (no

You disabled secure boot, or you enabled legacy boot (which requires you to disable secure boot)? Windows 8 machines typically won't boot off USB by default (not initing USB at firmware time saves a noticeable amount of time), but you can do it via the bootloader options menu without having to change any firmware settings