How can I boot by usb disk using S1200SPS board

I want my motherboard SP1200SP boot from usb disk.

So I had change the BIOS-

-> advanced

--> USB configuration

--> Mass storage device

  6000 : from auto to "Harddisk"

Then I can see my USB disk in the list of Boot maintenance Manager.

But Strangely, it still cannot boot from usbdisk.

Is there anything I had made wrong setting?

btw, what is the meaning of "6000" ?

Thanks you all!