Please can you give steps to disable the onboard

2.4.2 USB Configuration
The items in this menu allows you to change the USB-related features.
Select an item then press <Enter> to display the configuration options


USB Function [Enabled]
Allows you to enable or disable the USB function.
Configuration options: [Disabled] [Enabled]
Legacy USB Support [Auto]
Allows you to enable or disable support for USB devices on legacy
operating systems (OS). Setting to Auto allows the system to detect the
presence of USB devices at startup. If detected, the USB controller legacy
mode is enabled. If no USB device is detected, the legacy USB support is
disabled. Configuration options: [Disabled] [Enabled] [Auto]
USB 2.0 Controller [Enabled]
Allows you to enable or disable the USB 2.0 controller.
Configuration options: [Disabled] [Enabled]
USB 2.0 Controller Mode [HiSpeed]
Allows you to configure the USB 2.0 controller in HiSpeed (480 Mbps) or
Full Speed (12 Mbps). Configuration options: [HiSpeed] [Full Speed]
BIOS EHCI Hand-off [Disabled]
Allows you to enable support for operating systems without an EHCI
hand-off feature. Configuration options: [Enabled] [Disabled]

NOTE!!!

Do not disable the BIOS EHCI Hand-Off option if you are running a
Windows® operating system with USB device

hope above given details with give you a detailed description as you desired.

good luck

When you power up the computer press F1` or F2 or "del" key to enter in bios setup .
Then go to advanced configuration and disable usb controller.
Then save settings and exit from bios then onboard usb disabled
Let me know if you need further assistance.
Thanks for using FixYa.