The X99 board does not complete POST, it hangs at either A4 or B9 and makes a series of beeps.

This is normally caused by either a faulty USB hub (such as one found in a modern high end keyboard), a failed USB storage device (thumbdrive) or a USB device that is not making good connections, partially plugged in etc.

If this issue persists without USB devices attached, disconnect front panel headers, reset BIOS and retest.