h2s wont boot from usb to start flash any help please thanks


hi all
i try to flash h2s with open atv but every time just boot as normal not from usb , i try many different usb with 16 GB sandisk and no luck .the previous image is Ipab TV and i try to flash it with open atv , i did format the usb low level by soft ware the again low full level from windows and then insert the h3 file in and no boot form usb also did put the usb from back and then i turn the device on and preeing front bottom and no boot from usb , any help , thanks