Flash the newest uboot with a USB cable and flash tools then the image with the same procedure. The exact name of the image has to be usb_update.img . Sometimes Windows has deactivated the file extension that are commonly known, so you have to change that in folder options in your control panel to unhide it.
The USB cable has to connect with the USB Host connector.
If you have problems flashing with the USB stick, try formating it with the HP Formating utility.