I am dealing with a mobo shuttle hot 661v31.(atx)

I dont get to properly operate the front power button.
Under certain conditions¿? the system starts, and under others it just light
the power led and the hdd led, and remains that way with no response. The
monitor doesnot get to show anything.
Only when I manage the rear power bottom of the power supply the system
returns to normal operation
Any sugestion?
The manual  reads this:

"Dual Function Power Button -- The system can be one of two states, one is
Suspend mode and the other is the Soft-off mode. Pushing the power button
for less than 4 seconds will place the system into Suspend mode. When push
the power button for more than 4 seconds, the system enters the Soft-off
mode."

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