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?