The mordern motherboard has already built an onboard BIOS upgrade function called flashback.

However, there is some unexplainable phenomenon still keeping to happen in those motherboard and causing the motherboard shutdown forever.

The first generation of BIOS flashback is introduced in the early ear of 2015.
there is a BIOS Flashback buttom On X99 platform.

some users met the the flashback keeping to blink or flash with nothing wrong.
and it will finally make the motherboard unable to be reset, started or turned on.

here is the solution i found on Asus X-99/USB 3.1.
i have googled the issue on internet.
most suggestion would be "the take the battery of CMOS out", "use BIOS upgrade tool provided by manufacturer to upgrade BIOS" or "reseat everything you can seat".

those suggestions above are failed to fix the problem i got.

the issue is about the electric damage.

在主板側，Flashback按鈕的針腳因不明原因的靜電或殘存電器信號導致該按鈕被視為持續按下。
因此，一但關機後，Flashback按鈕會不斷閃爍等待BIOS更新檔從指定的USB埠被讀取。
進入此模式下的主板將被強迫停止啟動，直到Flashback從指定的USB埠讀出BIOS更新檔，並完成BIOS更新。
由此得知在主板側裸空的Flashback針腳應該被放電或短接，使持續按下的信號停止發送或是傳送出BIOS更新完成信號。

這是我跟該問題奮鬥五個小時後得到的結論。
我之所以打英語，是因為我發現網上沒有人有正確的解答。而本問題似乎沒有任何主板廠商有公開回覆處置方式。

再次提醒：我不為任何的損壞操作負擔責任，我僅只提供我所發現的解決方法。

so take the risk by your own.
i am not responsible for any damage if you met the same issue.
i just share the solution i found.