Is it an overheat or power supply problem?

At first, my 3 year old Inspiron 1150 started to have blue screens
with kernel_data_inpage. After a lot of trial and error and some
diagnostics, I replaced the hard drive. No more blue screens! Now my
laptop sometimes suddenly shuts down with absolutely no message. It's
almost like I press and hold the power button for a few seconds to
force it to shutdown except it doesn't have the short squeak sound the
force shutdown has right before the actual shutdown (not sure how to
describe that). It just silently powers off. The event viewer has
nothing. Before the shutdown, there's no warning. The only pattern I
can find is, I think it does this more when it runs CPU intensive
programs for a while, watching video, installing Oracle software, etc.

I just installed the wonderful i8kfan program (http://www.diefer.de/
i8kfan/). I'll try forcing the fan to run faster while I try to
install Oracle again. If it's not a temperature problem, could it be
the power supply? Any tips are appreciated.

Yong Huang
yong321 @ yahoo.com