PC randomly shuts down when Windows is loaded

[goroman]

Hi,
I am a PC tech for many years already but I have never seen this one.
Desktop PC worked totally fine. No hardware/software changes have been made to it. One day it just started to randomly shut down. No restarts, no BSOD, nothing, just shutting down. But it only shuts down when Windows 7 is loaded. If I use PC in Safe Mode, or do anything other than fully loading Windows, it works perfectly fine.
Steps taken:
Formatted HDD
Reinstalled Windows
Swapped RAM
Checked temperature of CPU, HDD, MB - none is getting hot
Unplugged/replugged all power connections to MB and drives
Disconnected all peripherals
Checked HDD, Video and Memory for errors - no errors found
Rechecked all fans

The logical thing would be power supply. If it is, then why wouldn't it fail when I don't load into Windows 7?
Another thing to check would be HDD. But again, why doesn't it fail when I don't load Windows 7?
And the final idea that I have is CPU. I'm guessing that when loaded into Windows, the cpu processes more than in safe mode for example and after reaching certain causes PC to shut down.
What are your ideas? What else can I check?

 

[Tmagic650]

"The logical thing would be power supply"... Instead of trying to find excuses not to try another power supply, this should be the first thing done with this sudden shut down symptom

 

[goroman]

"The logical thing would be power supply"... Instead of trying to find excuses not to try another power supply, this should be the first thing done with this sudden shut down symptom

I'm gonna do it today, however I still doubt this is the case. I'm leaning towards CPU....

 

[Tmagic650]

Did you get this fixed?

 

[goroman]

Did you get this fixed?

Yeahhh...it was power supply. Very weird. It would work flawlessly when Windows is not loaded.

 

[Tmagic650]

Okay, thanks for the update... and happy computing