Unexplained computer shutdowns

[Jagwire J]

I have been troubleshooting a computer lately that has been plagued by occasional shutdowns without warning. There is no BSOD, the machine simply shuts down after a period of use. Since this computer was extremely dusty, I assumed that a thermal shutdown was occuring and cleaned it out, but the problem still persisted. I then checked the psu manually with a paperclip, and all of the outputs on the 24 pin mobo connector had the correct voltages (12v 5v and 3.3v). There have been no hardware changes or upgrades either. As a matter of fact, the computer is completely stock so the psu should have the propper wattage and all of the clock speeds are unaltered (no overclocking). After a recent shutdown, the computer still passes the POST test, can boot into bios by pushing the correct function key, but boots automatically into the windows recovery screen. When in the recovery environment, the os does not recognize the keyboard or mouse inputs, but I know the usb ports are working because the peripherals work in the BIOS. Could the PSU be failing even though the 24 pin connector outputs the right voltages? Or could the motherboard possibly be dying? The computer is about 5-6 years old so bad components are very possible.

 

[DSzymborski]

If the temperatures are fine, then the PSU is the next suspect. Just because you're getting the right voltage readings doesn't remotely mean a power supply isn't failing - sudden shutdowns, when not due to heat, are very commonly due to power supplies failing at load.

 

[Jagwire J]

This time i decided to take a different approach. I loaded up prime95 to stress out the cpu and psu at the same time. Software voltage monitors like cpuz kept throwing wierd voltages at me, so i broke out the voltmeter and manually tested the voltages under load. There was no shutdown and the voltages checked out. This time it shut down while trying to simply transfer files. The screen blacks out but all of the fans continue to run. The OS also appears to shut down because the data was being transfered from an external hard drive, and the status light quit blinking. The files were way too big to be done transferring so i know it was cut off.

 

[Jagwire J]

Also, this is occuring on a custom install of windows 10.