[sohyun]

Hi Mac experts,
I've got a 12 inch powerbook (about 3 years old) from my friend
recently. It perfectly works about 1 hour and then it keeps turning
into sleep mode (not shut down) when just starting fan sound. It looks
the computer is unable to take heat!!! I googled about this issue. One
of answers grabbed my eyes which dust around cooling fan in the laptop
caused the problem. Do you have any idea why it does like it? Thank you
in advance for your answers.

[rab777hp]

You might want to move this to the mac 911 thread, however this sounds like a battery issue, 3 years is definitely time to replace batteries. That's what it sounds like to me.