iMac won`t power on. Power button pressed = LED # 2 lights up briefly
I currently have an iMac 27 "5K Late 2015.
The iMac will not turn on.
Diagnostic LED # 1 lights up when the Mac is powered.
As soon as the power button is pressed, LED # 2 lights up briefly and goes off again.
There are no fans running.
Power supply is fine.
Someone an idea?