Most modern computers are enabled to boot from CD and USB drives. This setting is configured in the computer's basic input/output system, or BIOS. The BIOS is the initial program that runs prior to Windows startup. To disable Boot From USB, you will access the BIOS and disable the setting in the Startup Options in the BIOS. In most cases, pressing the delete or F2 key, when prompted, will open the BIOS for configuration. The key prompt will appear early in the boot-up process.
Reboot the computer.
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Press the "Delete" key, the "F2" key or the key that is indicated early in the boot-up sequence. The first screen of the BIOS opens.
Page to the "Startup Options" section of the BIOS. For some BIOS programs, "Alt" + "P" will page to the next section. In others, use the right and left arrows. Instructions are usually posted for paging and changing selections.
Deselect or disable the "USB Boot" option.
Save the settings and exit the BIOS. The computer will reboot and boot up normally. Often, the F10 button will save the BIOS settings and exit.