iMac was dead after update 15.4.1 with OCLP

After some several reboots, it not doesn't response to anything when I press the power button on. I'm not so sure whether because of the new update or what's the cause.
P/S: When I tried to plug in my gaming keyboard, the RGB light is still on, but there's nothing going on with the iMac. Any thoughts? Thanks.

Author: @hoangdj