Unexpected shutdown if system service "power" is running

so my computer started unexpectedly shutting down about 60 seconds after loading windows today. No BSOD, no error message, no warning, just a hard shutdown. It happened consistently every time I started the computer, unless I was in safe mode, then I had no issues. So I went into msconfig, and eventually tracked the problem down to a specific system service - "power". If that process is stopped, no hard shutdown. But that process seems to be responsible for Windows Audio Endpoint Builder, so I have no audio if it is stopped. Can anyone think of any reasons for this process to cause an unexpected shutdown? and how do I go about fixing it?

alright, followed the guide and turned on verifier, but I ended up with the same hard shutdown, still no BSOD or error message of any kind. also no DMP file in the minidump folder (that's C:\Windows\Minidump right?) not sure what to make of this. . .

alright, still no luck getting a minidump after that last suggestion. But through trial and error, I found that I can make the unexpected shutdowns stop if hyper-threading is disabled in the BIOS; on the down side, that seems to make my computer only recognize two cores on my quad-core processor, instead of all four. I don't see how hyper-threading and this particular system process could be related.

Asus P5N-D, CPU is a Core 2 Quad Q9550, and the BIOS is the latest version.

I'm totally stumped. I even rolled back to a previous BIOS, but no difference.

my laptop automatically shut down after a few hours, and i have checked power setting and i didnt see any unusual thing !
please help me! tanx