my R405-A cant help but shutting down

hi
ok its my first post here

ok got a big prob...
recently i got a lg r405a cuz my old vaio died..
it has a core 2 duo t5450, 2gb, 200gb, ati video card...+vista home premium

but my lg power off itself without any notice
just like it would when the power key is hold down but actually without the power key being touched at all..
it just shut off
and i cant turn it on for ~5 minutes
all the lights goes off even if battery/ac is plugged in
usually when the ac is plugged and the laptop is turn off the ac and battery light would be light on but no in this case...

and also the first time it happened i thought it was some hardware problems
so i took it back and got it exchanged and it keeps happening
at least once a week...every saturday i think..
it just happened like some minutes ago
and i was using a laptop cooler ...lapcool3 by vantec with laptop fan set at cool mode..

anyone has a guess??
thank you

 

I'll be honest, that's pretty strange. My LG R405 doesn't have that problem

 

i realize that it happen when i plug my mouse into the usb behind 'just under the power button'
and when i lift the laptop so that from the side it looks like a V it goes off