Laptop powers up without pressing the power button, and restarts

[Aneez]

i've got a problem with this HP nx 6110, that it turns on without at all touching the power button. and in a few seconds tries to restart. there is no display at all.
I suspected a battery problem, so i removed the battery.
I've subsequently opened the laptop completely, and step by step removed each component. now i'm left with just the motherboard with the processor (no CMOS battery either), to which the power cable is connected. but still it's just the same old problem.

i turn the switch on.  the AC main light turns on, then in a few second, the other light tuns on, and the fan starts spinning, after a few seconds, all the lights go off, the fan appears to be stopping, but before it completely stops spinning, the whole process repeats, starting from the AC light turning on.

i suspect the motherboard, but somehow i'm sure there is something that can be done.

any ideas welcomed.

[Quantos]

Is this laptop still under warranty?

[Aneez]

No, it's around 4 years old.

[Quantos]

I suspect that there is a motherboard failure, but don't run out and replace it just yet.  I'm not fully awake(only third cup of coffee), someone else may have an idea.

[patio]

Unfortunately laptops are not meant to be user serviceable...
I'd get a quote from an Authorised service center.