Why do people go to BIOS settings, change them, then change back again? You can also press F11 (or another button in the Boot Menu) and choose USB flash drive. But after rebooting again will boot the first hard, as it should be.
But the question is what can I say? Or Windows non-bootable or non-bootable USB flash drive (recorded incorrectly as if)...And even if you are sure about, that anything can happen, perepesi try again.