power button not working

Most likely the system board is failing.

i don't think so, b/c system working fine, once it started successfully.
i think it is only matter of power button.

I am having an identical problem with my Inspiron 9300. The power light turns on, but the laptop does not enter the usual boot sequence on frequent occasions, rather the screen remains black. The same problem occurs with or without a power cable connected.
Sometimes, if left to its own devices, it will suddenly start to boot from this state.

Any help would be greatly appreciated.

It has been suggested that it may be a problem with the system board failing. Can anyone be more specific? How is the boot initiated from when the power button is pressesd?

Thanks again in advance