If Fast Boot is enabled in UEFI/BIOS, you may not be able to boot from a USB flash drive unless you boot from the USB within Windows; otherwise, you will have to temporarily disable Fast Boot or ...

FAT32 (File Allocation Table 32) is a file system format for storage devices such as USB flash drives ... Many systems, including BIOS-based systems and some UEFI systems, can boot from a FAT32 ...